It can be a delight or a disappointment to see one's favorite celebrity grace the small screen. Perhaps the most important genre any star can appear in when choosing a TV role is sitcom. Whether appearing as fictional versions of themselves, creating a brand-new character specifically for the show, or even reprising a former character in a crossover, seeing a famous face on a sitcom can be a highlight of any show -- sometimes, at least.

Like any type of show, bringing a celebrity to the small screen isn't always a great idea and can feel unnecessary, irrelevant to the plot, or downright embarrassing for other characters, the story, and the overall situation(s) the actor is forced to take part in. This leads to an important lesson to remember: it's not always the celebrity's fault. Everyone on this list is talented and has legions of fans, but this doesn't mean that all of them were meant to try their hand at TV comedy.

Even sitcoms that have become synonymous with celebrity appearances, like The Simpsons and Curb Your Enthusiasm, have had their ups and downs and have (hopefully) realized that they can't just bring in any celebrity and expect it to be funny. So, today, let's see if these celebs had what it took to make it on comedic TV or if they should've stuck with what they were good at (i.e., anything else).

With that said, here are the 9 A-Lister Cameos That Hurt Iconic Sitcoms (And 11 That Stole The Show).

Stole The Show: Carrie Fisher - 30 Rock

The late Carrie Fisher was adored by many for her iconic portrayal of Princess Leia Organa in the Star Wars franchise. However, some fans are unaware of her other achievements, including a posthumous Grammy Award for Best Spoken Word and three Emmy nominations, one of which was for a memorable guest appearance on 30 Rock.

Since Star Wars is frequently referenced in the series and Tina Fey's Liz Lemon is a huge fan of the franchise, it only made sense to cast Fisher as Lemon's idol, author Rosemary Howard. In the hilariously-named second season episode "Rosemary's Baby", Lemon wants to have Howard as a guest writer on her show... until she finds out how crazy her ideas are. While Fisher's appearance as herself on The Big Bang Theory was hilarious, many fans will prefer this lengthier appearance.

Hurt: Jean-Claude Van Damme - Friends

Rachel Talks to Jean Claude Van Damme and asks him out for Monica in Friends

Action superstar, award-winning martial artist, and sitcom guest actor -- yeah, we don't think that matches either. Jean-Claude Van Damme has certainly had an interesting career, with countless movies to his name and a reputation as one of Hollywood's toughest action heroes. So, it came as a surprise when Van Damme appeared as himself on long-running sitcom Friends.

Van Damme wasn't the only celebrity cast in the two-part episode "The One After the Superbowl", as Julia Roberts, Fred Willard, and Brooke Shields also appeared. However, Van Damme's stands out for how poorly he delivers his lines, using his accent and poor emphasis on words to little comedic effect. Sorry, Van Damme, but how Rachel and Monica could stand being around you is a mystery.

 Stole The Show: Idris Elba - The Office (U.S.)

Some celebrities are invited onto sitcoms for a recurring role, which can be better or worse than a one-off appearance. In the case of Golden Globe winner Idris Elba, this was definitely a good call, as his no-nonsense character of Charles Miner could not be contained within only one episode of The Office.

First appearing in the season five episode "New Boss", Miner takes over for Ryan Howard as Vice President of the Northeast Region. However, he comes to hate Jim and clash with Michael (which leads to his temporary resignation). While Elba played the part of an unlikeable character very well, he also provided a source of office conflict the show needed and stuck around for an additional six episodes throughout the season.

Hurt: Kathy Bates - Two and a Half Men

After lead actor Charlie Sheen was cut from Two and a Half Men, many fans will argue that the show's remaining four seasons failed to live up to its previous eight with Sheen. However, his character of Charlie Harper did return in season nine... just not the way fans imagined.

In the episode "Why We Gave Up Women", Charlie's ghost (portrayed by Oscar-winning actress Kathy Bates wearing one of Charlie's shirts) appears to Alan in the hospital, explaining that he's been sentenced to an eternity in Hell due to his life of debauchery and must live it out as an obese elderly woman. Although it won Bates her first Emmy, it doesn't make the role any less terrible. Despite Sheen's misbehavior, his character was beloved by fans, and there was no need to see Charlie meet such a sad end.

 Stole The Show: Sir Ian McKellen - Extras

While they are most remembered for the UK version of The Office, comedians Ricky Gervais and Stephen Merchant also co-created/directed Extras, which also ranks among the best UK comedy shows. Centering on movie extra Andy Millman (played by Gervais), the series featured various celebrities playing alternative versions of themselves, and, while Sir Patrick Stewart's lewd version of himself is usually the most remembered, Sir Ian McKellen's role definitely earns a mention.

On a hunt for a theatre role, Andy meets up with McKellen, who is directing a gay romance entitled "A Month of Summers." When discussing it with Andy, McKellen takes it upon himself to review the process behind acting in the most descriptive and oblivious way possible. The result is comedy gold and even includes a Gandalf line, which makes McKellen all the more deserving of his Emmy nomination.

Hurt: Martin Sheen - The Simpsons

The Simpsons deserves a ranking due to its vast number of guest stars. While many did well on the show, other celebrity roles seemed unnecessary. Unfortunately, Golden Globe winner Martin Sheen's guest spot in season nine warranted the latter.

In "The Principal and the Pauper", Principal Skinner is revealed to be a fraud after the real Seymour Skinner (voiced by Sheen) arrives in Springfield to take over his job. However, the townspeople don't get along with him and end up banishing him in the end, giving the old Skinner (whose real name is Armin Tamzarian) his life back. While there's nothing wrong with Sheen's performance, the revelation that an iconic long-running character was a phony didn't sit well with many, including series creator Matt Groening.

 Stole The Show: Betty White - My Name is Earl

Honestly, when does Betty White not steal the show? The multi-Emmy winner has been on TV for eight decades but never shows signs of slowing down. While White has appeared on multiple sitcoms, we're highlighting her guest spot in season four of My Name is Earl as Grizelda Weezmer, an old lady Earl who the gang call a "crazy witch lady."

When Earl goes over to her house to apologize for harassing her during his youth, she locks him in her basement, seeking revenge on her tormenters. However, Earl eventually apologizes and is sent to a psychiatric institution. While this isn't what fans are used to from the loveable White, seeing her as a tragic villain made her stand out in the episode. Also, there's a happy ending and plenty of humor, as all Betty White programs have.

Hurt: Katharine McPhee - Community

Singer Katharine McPhee may have placed as a runner-up on American Idol, but her character in Community's debut season ranks among one of her worst acting roles. Titled "Basic Genealogy", the episode sees McPhee as Pierce's step-daughter Amber, who begins a relationship with Jeff. However, she soon reveals that she's been stealing money from Pierce, who's been trying to spend time with her, which results in her and Jeff breaking up and her leaving.

While the episode does end with a touching moment between Pierce and Jeff (and the rest of the gang are up to their own hijinks, as usual), McPhee's character comes off as forgettable, despite having a past with one of the main characters. If fans really want to appreciate McPhee's acting talent, they should just check out Smash instead.

 Stole The Show: Seinfeld Cast - Curb Your Enthusiasm

Ever since the disappointing finale of everyone's favorite "show about nothing," fans have clamored for a reunion. When a show starring a fictionalized version of co-creator Larry David premiered back in 2000, fans saw a glimmer of hope. While it may have taken seven seasons, this glimmer was soon made a reality.

Over the course of three episodes, Seinfeld stars Jerry Seinfeld, Julia Louis-Dreyfus, Jason Alexander, and Michael Richards appeared as themselves, culminating in the appropriately-titled season finale, "Seinfeld". However, while the show's reunion special (which takes place several years after the original series) gives fans what they want, the "real life" events with the cast (Alexander publishing an incredibly-short book on acting, Richards' fear of black people following his 2006 outburst) are arguably what truly make the episodes so memorable.

Hurt: Michelle Obama - iCarly

Michelle obama on iCarly

Michelle Obama remains one of the country's most admired women. However, that doesn't mean her season five guest spot on Nickelodeon's iCarly would be admired by viewers. The episode deals with Carly wanting to see her dad, an Air Force colonel serving overseas, on his birthday. When he is unable to make it, the iCarly crew sets up a video chat, which is discovered by Obama.

Though, instead of having them arrested, she praises their efforts, as well as Carly's kind words to her dad about his service. Though Obama was clearly trying to show support for military families, the episode focused more on her appearance rather than the message. Perhaps she'll have better luck producing for Netflix alongside her husband.

 Stole The Show: Stephen Hawking - The Big Bang Theory

The Big Bang Theory is winding down this year in its final season (at least we still have Young Sheldon) and fans are already reminiscing on their favorite moments from the show's 12-year run. While there were a lot of great guest stars, arguably the one that won over the most fans was the late theoretical physicist Stephen Hawking.

From the moment he first appeared in the season five episode "The Hawking Excitation" to point out an arithmetic error in Sheldon's paper, Hawking established himself as one of the show's greatest guests. Following this, he guest-starred in six more episodes, doing everything from bragging about beating Sheldon at Words with Friends to singing at his birthday party. Hawking defied odds with his long life, and he more than defied expectations with his role on this show.

Hurt: Joe Namath - The Brady Bunch

There's no denying the fact that Joe Namath has become an inspiration for many with his football status in the AFL and NFL. However, what could've been a memorable spot on one of the US's most iconic series turned into a moment best forgotten in his career

In the final season episode "Mail Order Hero", Bobby hears that the New York Jets are coming to town and brags to his friends that he knows Namath. When they ask for proof, Cindy writes to Namath that Bobby has a serious illness and would like to meet his hero, which results in Namath showing up to visit him and Bobby having to back up the lie by acting sick. While some fans may still enjoy the episode overall, others will probably find Cindy's actions too surprising to permit any redeemable elements.

 Stole The Show: Susan Sarandon - Friends

Friends has had a plethora of great actors appear, and Oscar winner Susan Sarandon's role as fictional Days of Our Lives actress Cecilia Monroe in season seven is one of the greatest (she was nominated for an Emmy, after all).

In "The One With Joey's New Brain", Joey finds out that his Days of Our Lives character, Drake Ramoray, will be awoken from his coma after receiving a brain transplant. Wanting to know how the previous character acts, he consults with the actress, not knowing that she was unaware her character was being cut off. Despite her anger, she agrees to help Joey and they soon begin a relationship. While the relationship doesn't last long, seeing Joey interact with a star of Sarandon's caliber was a definite treat.

Hurt: Jaleel White - Full House

Steve Urkel from Family Matters

While TV crossovers certainly still happen today, in the 20th century, they were so abundant that fans needed two lists to keep them all straight: the good and the bad. While Jaleel White's Family Matters character Steve Urkel was a delight, he appeared on Full House for the wrong reasons.

In the season four episode "Stephanie Gets Framed", Urkel is revealed to be related to D.J.'s friend Julie and happens to be in town for a science fair at the same time Stephane is told she has to get reading glasses. Besides irritating much of the cast (as usual), Urkel gives Stephanie some advice about wearing glasses (even though it's ultimately Joey who convinces her to embrace them). "Unnecessary" is the word to describe Urkel's cameo, as any other bespectacled character could've done the job better.

 Stole The Show: Sinbad - It's Always Sunny in Philadelphia

Comedian Sinbad may not be as well-known as he was in the '90s, but the man hasn't lost his funny side. Take his appearance in It's Always Sunny in Philadelphia's fourth season episode "Dennis Reynolds: An Erotic Life" for example. In the episode, he's being held in a rehabilitation center along with Dennis and Grammy-winning Matchbox 20 lead singer Rob Thomas... and that's all you need to know.

From a memorable headshot to his demand that Thomas "sing a song" before immediately telling him to "shut up," Sinbad's comedic talents are on full display for both old and new fans, making this guest spot just as crazy and hilarious as the rest of this long-running cult series.

Hurt: The Beach Boys - Home Improvement

Some musician cameos in sitcoms are memorable and funny, allowing artists to poke fun at themselves and their music. However, when the Beach Boys decided a cameo in Full House wasn't enough, they went on to appear in Home Improvement's sixth season, and the results were certainly no day at the beach.

Appearing as themselves in "The Karate Kid Returns", the band was revealed to be related to Wilson, because, of course, any characters that share last names with celebrities must automatically be related. Fans of both the show and the band certainly weren't feeling any "Good Vibrations" after viewing this bizarre episode, however. Even worse, the episode aired a little over a year before the passing of co-founder Carl Wilson, which had a big impact on the group moving forward.

 Stole The Show: LeVar Burton - Community

Emmy winner LeVar Burton has developed legions of fans through his hosting time on Reading Rainbow and his role of Lieutenant Commander Geordi La Forge in the Star Trek franchise, with one of the biggest being Troy Barnes from Community.

In the second season episode "Intermediate Documentary Filmmaking", Pierce arranges for Burton to meet Troy, despite Troy telling him he never wanted to in fear of embarrassing himself in front of him. When they meet, Troy is stunned and can't speak for the rest of the day, and eventually runs away screaming. Burton would later reappear in season five's "Geothermal Escapism", in which he joins Troy on a worldwide sailing expedition. Since this was actor Donald Glover's final episode, Burton's company added another level of heart to the sendoff and solidified his place in the show's history.

Hurt: Jermaine Jackson - The Facts of Life

While this spinoff to Diff'rent Strokes was very popular, it certainly had a bizarre assortment of guest stars, ranging from Zsa Zsa Gabor to David Spade. However, when Kim Fields' Tootie was revealed to be a diehard fan of a musical guest, audiences probably raised their eyebrows when it was revealed to be for Grammy nominee and Jackson 5 member Jermaine Jackson.

Out of all of the '80s musicians who young girls were swooning over, the show decided to go with one of the lesser-known Jackson brothers in season three's "Starstruck". Not only that, but Tootie's obsession with Jackson gets downright uncomfortable at times, with her having a fit to get Mrs. Garrett to take her to his concert. All in all, it's not a bad episode, but Jackson's appearance certainly didn't make it a memorable one.

 Stole The Show: Regis Philbin - How I Met Your Mother

How I Met Your Mother had too many guest stars to count, but some definitely stood above others. While not the lengthiest or most relevant cameo in the series, multi-Emmy-winning host Regis Philbin's appearance in "The Best Burger in New York" was a highlight of both season two and the series overall.

Marshall and the gang search for a burger restaurant he claims is the best in New York, even asking Philbin himself (who's also passionate about finding it). Unfortunately, they hit several road blocks, with each making Philbin (who left in the middle of a TV recording to meet up with the gang) angrier. While they do find it in the end, Philbin's anger outbursts are a delight to watch. Whether he's demonstrating his strength to Barney or yelling "Onions?!" into a cellphone, he own every scene he's in.

Stole The Show: Danny Pudi - Cougar Town

Sometimes, it's the simplest cameos that make the biggest impact. Such is the case with Danny Pudi's reprisal of Abed Nadir from Community on Cougar Town.

In one of the greatest crossovers ever, Abed tells Jeff in the season two episode "Critical Film Studies" that he recently visited the set of Cougar Town (his favorite TV comedy) and got to play an extra. Two months after the episode aired, Cougar Town's second season finale featured Abed sitting at a table behind Laurie and Travis. While Pudi never interacts with the characters, Abed makes himself look hilariously out of place in the background. To top it off, actors Dan Byrd and Busy Phillips (Travis and Laurie) also appeared in Community's second season finale, bringing the crossover full-circle.

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Are there any other a-lister cameos that hurt or saved iconic sitcoms? Let us know in the comments!