One of the best things about The Big Bang Theory is that no matter how much the main characters transform and grow over the years, they're still incredibly similar to the people whom viewers' first met in season 1. Characters like Amy and Bernadette have shifted personality-wise since their first episode, but they're consistent in morals and logic.

However, there were rare moments when the main characters said things that didn't align with their personalities. Everyone from Howard to Penny reacted in ways that seemed odd when looking at their overall character.

Updated on August 25th, 2022, by Lynn Gibbs: The best Big Bang Theory quotes are some of the smartest and funniest lines from sitcoms ever. With the core four being scientists, their witty responses to situations made for entertaining episodes. The Big Bang Theory only got better when Penny, Bernadette, and Amy hung out with the group more consistently. But with 12 seasons to Big Bang Theory's name, the main characters were bound to have moments or quotes that didn't match their characters.

"I Know I'm Not The Warmest Of Parents..."

Beverly Hofstadter - 'The Conference Valuation'

Leonard Hofstadter tearfully embraces his mother Beverly in The Big Bang Theory

Beverly Hofstadter was not the warmest of mothers to Leonard. As a neuroscientist and psychiatrist, Beverly studied her children and ran experiments while producing parenting books on her research. Leonard always hated that he didn't have the warm, affectionate childhood that so many children deserved.

RELATED: Leonard & Beverly's 10 Worst Mother-Son Moments On The Big Bang Theory

However, in 'The Conference Valuation,' Beverly said something that was out of character: "I know I'm not the warmest of parents, but it was time we spent together... Those are some of my fondest memories." Considering Leonard thought his mother disapproved of him, this was a shock. Maybe TBBT's Beverly wasn't that bad?

"Angular Momentum. I Was Wondering About That."

Zack Johnson - 'The Fermentation Bifurcation'

Zack at dinner with Penny and Leonard on TBBT

Penny had dated quite a few men before settling down with Leonard, and one of those men was Zack Johnson. Zack was someone Penny dated to get over Leonard, but the two never had a serious relationship because he didn't stimulate Penny intellectually.

As a dimwitted character, Zack said silly things often and was rarely serious. And even though he was interested in comics and physics, he didn't fully understand both. However, he had a moment of brightness in 'The Fermentation Bifurcation.' Zack asked the group what their invention was. After Howard and Leonard explained the complexities of their project, Zack surprised everyone by understanding and mentioning angular momentum. It was out of character for him and made fans laugh out of surprise.

"When I Was Your Age You Could Have Me For A Car Ride And A Bottle Of Strawberry Wine."

Mary Cooper - 'The Rhinitis Revelation'

Mary Cooper looks through penny's laundry on the Big Bang theory

In 'The Rhinitis Revelation,' Sheldon's religious mother came to visit him and his friends. Mary had some outlandish quotes throughout TBBT because they were often judgemental, out of touch, and stereotypical. But as a die-hard Christian, Mary said something to Penny that was out of character.

While doing laundry with Penny, Mary questioned a piece of lingerie Penny had. She assured Mary that not every man she brought him got far enough to see her lingerie, which led Mary to say this quote about strawberry wine and a joyride. It's hard to imagine Mary being so free-spirited with both alcohol and men. It was a side of her that fans never saw before.

Penny: "Is This Me?" Stuart: "Depends, Do You Like It?"

Stuart Bloom - 'The Hofstadter Isotope'

A split image of Penny and Stuart with her drawing on TBBT

When viewers first met Stuart, it was Penny's first time meeting him as well. After a quick meeting, Stuart appeared cool, calm, and confident as the owner of the comic book store that the guys frequented. While Leonard had a hard time flirting with Penny in season 2, Stuart had no issues.

RELATED: Stuart's 9 Best Quotes From The Big Bang Theory

When Penny asked Stuart if a picture he was drawing was her, Stuart said all the right things that kept Penny flattered and interested. Compared to the Stuart fans got to know in later episodes, this entire exchange was out of character. It didn't make sense that Stuart went from a smooth ladies' man to someone so down on his luck.

"I've Been Thinking That Given The Parameters Of Your Experiment..."

Penny Hofstadter - 'The Gorilla Experiment'

Split image of Sheldon teaching Penny physics and next to Penny on TBBT

When Penny and Leonard began dating, Penny wanted to understand what Leonard did for work. With physics outside the realm of Penny's understanding, Sheldon promised to teach her a thing or two. Penny didn't care what opinions others had of her dating Leonard, but she wanted to at least understand what he did for work.

After a long and tiring lesson from Sheldon, Penny learned two long-winded sentences that she recited in front of the group.

"I've Been Thinking That Given The Parameters Of Your Experiment, The Transport Of Electrons Through The Aperture Of The Nano-Fabricated Metal Rings Is Qualitatively No Different Than The Experiment Already Conducted In The Netherlands."

What she said was true but completely out of character, which was why the group had their tongues hanging out of their mouths as she spoke.

"Right. Just Kissing. It Wasn't Even Very Good. She Was A Smoker. I'd Just Been Seasick..."

Leonard Hofstadter - 'The Commitment Determination'

Leonard and Penny in the hotel room talking on TBBT

It was a smart career decision for Leonard to go away at sea to work with Professor Stephen Hawking's scientific group as he would be a part of history if their experiment went well. But the trip seemed to be more play than work for Leonard.

When Leonard came back from sea and was about to walk down the aisle with Penny, he admitted that he had cheated on her while he was on the ship. Everything he was saying was completely out of character because he had fought to be with Penny for years. Why would he throw it away for a kiss at sea? Penny (and fans) were disappointed with Leonard because that decision was out of character.

"We Lock That Door, Lower Our Underpants A Little, And Make A Baby."

Sheldon Cooper - 'The Brain Bowl Incubation'

Sheldon shows Amy their experiment's results on TBBT

It took Sheldon years to be comfortable enough with Amy to call her his girlfriend. It took him even longer to ask her to marry him. But somewhere along their rollercoaster of a relationship, Sheldon and Amy did an experiment on the combination of their genes. Seeing how brilliant the results were, Amy couldn't wait to replicate the results. Sheldon, on the other hand, had another idea: he wanted to make a baby.

The realization that they could produce a genius made Sheldon excited. But hearing him say, "We lock that door, lower our underpants a little, and make a baby" was one of the best, albeit, shocking Sheldon quotes. Some of the best Sheldon Cooper quotes were out of character for him. Sheldon was not fond of personal intimacy, so for him to want to procreate was uncharacteristic of him.

"She Wants A Commitment And I'm Not Sure She's My Type."

Howard Wolowitz - 'The Vengeance Formulation'

Howard in the tub with Katie Sackhoff in TBBT

When Howard and Bernadette first started dating, Howard slowly stopped answering her calls. The ups and downs of their relationship were relatable for viewers, but fans couldn't help but wonder if Howard realized how good he had it with Bernadette.

RELATED: 10 Ways Howard & Bernadette Are The Most Relatable Couple From The Big Bang Theory

Howard was always trying to land himself a girlfriend, and when he finally had one that was as beautiful and smart as Bernadette, it was odd that he was suddenly not fond of "commitment." Out of all the men, Howard was the most desperate for affection.

"Koothrappali Out. God Bless That Boy, I Don't Know What I'd Do Without Him."

Raj Koothrappali - 'The Griffin Equivalency'

Penny talking to Raj at the Cheesecake Factory on TBBT

If there's one thing that fans would change about Raj's storyline in TBBT, it would be that he got the happy ending he desperately wanted since season 1. He wanted a wife and kids more than his friends.

In an episode where Raj won an award from People Magazine, his personality shifted. He suddenly thought he was better than his friends and could get any woman he wanted. In one scene, he was on the phone talking to his assistant and sounded cocky, making his friends watch in disgust. It was rare for viewers to hear Raj say "Koothrappali out" on the phone, or even rely so heavily on an assistant he had for one day.

"You Should Know That All Forms Of Physical Contact Up To And Including Coitus Are Off The Table."

Amy Farrah Fowler - 'The Lunar Excitation'

Amy and Sheldon at the movies in The Big Bang Theory

Amy is one character who changed the most throughout the series. She transformed from a robotic and shy woman to someone who was outwardly sexual and spoke her mind.

At the start, Amy told Sheldon that "all forms of physical contact" were off the table. This is incredibly out of character for the Amy fans knew in season 12 because Amy practically begged Sheldon for hugs and forms of intimacy. It's hard to picture her not wanting to sleep with Sheldon when she asked him to get physical with her for years.

"Does She Pick Your Clothes For You In The Morning Like You're Nine Years Old?"

Bernadette Rostenkowski-Wolowitz - 'The Creepy Candy Coating Corollary'

Howard and Bernadette on their first date on TBBT

When Bernadette and Howard go on their first date, the only thing the two have in common is their overbearing mothers. The two shared stories of how dominating their mothers were, with Bernadette claiming her mom still picked out her clothes.

This was strange for her because as fans got to know Bernadette, they saw how independent she was. Her mother was rarely in her life and she judged Howard for how close he was to his mother. The inconsistent quote from Bernadette was out of character for her because it didn't match her reality.

NEXT: 10 Hidden Details About Bernadette Everyone Missed In The Big Bang Theory