For a long of people, King of The Hill is a classic comedy that stands the test of time. The writers did a great job making it an honest slice of middle-American Texan life while it was on. It treated things when delicacy when needed (most times) and didn't fear pushing the envelope on others. The storylines reveled in Hank Hill's idiosyncratic ideals, Bobby Hill's perpetual middle-school awkwardness, and Peggy Hill's authoritarian version of wife/motherhood.
However, while most of the show hold up for modern audiences, some of its running jokes don't. Too many socially progressive movements have happened for that not to be the case. Might as well look back and talk about the humor that wouldn't fly in a 2019 show.
Bobby Creeping On Luanne
When young and beautiful Luanne moved in with her aunt Peggy's family, there was a quick unintended consequence: young Bobby's infatuation with her. However, Bobby's feelings for Luanne go a bit far. It starts with light, middle school stars and flirting. Over time, though, it turned into all-out creepy stalking. Bobby would sometimes go so far as to watch her sleep or try to see her naked.
Worse, the show also makes it clear that the two do see each other more like siblings, so the bizarre antics are a splice of "young boy being too creepy" and kind of incest-y. Shows today probably wouldn't include these kinds of jokes, not without making it clear that behaving like that is pretty unacceptable and gross.
Foot Exploitation
In the episode Transnational Amusements Presents: Peggy's Magic Sex Feet, Peggy's doctor takes an interest in her size 16 feet. While she thinks she's doing foot modeling, he's actually recording her feet doing odd things for foot fetish porn. Similar to the Meg foot fetish episode in Family Guy, at the time, it could be funny to make fun of the insecure person by giving them false confidence.
However, the real uncomfortable angle is that, in the case of both Peggy and Meg, their feet were used for pornographic reasons without their permission. Turning someone else's feet into a sexual object is pretty gross without their consent. People would probably revile that kind of episode-long joke nowadays.
Ugly For The Money
Dale and Nancy's tumultuous and strained relationship is already not very funny, but the show reaches peak discomfort in The Trouble With Gribbles. In a bid to win money to make the aging Nancy feel better about herself, he files a lawsuit against a cigarette company, saying second-hand smoking has made her ugly.
To seal the deal, even though the money is "for her," he convinces Nancy she's ugly to make the suit believable. Of course, this only makes Nancy feel all the worse about aging. The point was to make a joke about of the hijinks Dale went through and how it affects her. Audiences now, though, would probably just focus on the horrible tragedy of their marriage and how awful it was that Dale made her feel that way. He could have just let her in on the con, right? He didn't need to make her feel awful.
Discouraged Bobby
A running theme throughout King of The Hill is that, while Peggy and Hank love Bobby, he's not exactly the son they dreamed of. They wanted more of a sporty athlete with good social skills. Instead, they got a boy who likes home ec., Dance Dance Revolution, Buddhism, and other unconventional hobbies.
However, his parents almost always disapprove. Sometimes, this turns into a great teaching moment where they learn to accept Bobby, quirks and all, but others end on bizarre, "funny" notes. For example, Peggy hijacking the Thanksgiving turkey he makes and giving it to someone else, or Hank Hill calling soccer a sissy game that European women made up. They can accept Bobby, but they still do questionable things to him and scorn some of his interests. Current audiences would prefer they accept their son no matter what weird things he was into and wouldn't appreciate the soccer jokes very much.
Kahn's Bipolar Disorder
Kahn is Hank Hill's next-door neighbor, a man from Laos who just wants to live a normal life in America (with an immaculate lawn to top it all off). However, later in the show, it's revealed that Kahn has Bipolar Disorder.
The show doesn't handle it too well. While it doesn't make fun of him, per se, Hank does manipulate Kahn and use his mania to put a grill together. The episode pokes fun at his rapid-cycling moods and the way his moods completely swing out of control. All it took, according to the show, was a few days off his meds. Since that isn't how Bipolar Disorder really works, these jokes wouldn't have aged very well for modern audiences.
Self-Righteous Peggy
The core humor of Peggy Hill is her self-righteous nature. She is very sure in her own wisdom and ideals, which can get strung out into comedic situations. However, this also was a common reason why fans hated her with a passion, even during the show's run.
Nowadays, her shtick would age very poorly. For example, her giving away a nice Turkey that her son made for Thanksgiving, just because she believes that cooking and housework are her job, not his, wouldn't go over well. Old school fans often rejected this episode for being cruel and unfunny, so modern fans definitely would hate it.
Luanne's Dating Life
All throughout King of The Hill, Luanne's choices in men are always played for a joke. Whether it's her brief fling with Boomhauer, the mismatch between her and the much older, much uglier Lucky, or the infamous Pigmalion episode, her dating life is a source of comedy.
However, those jokes probably wouldn't age well. Sure, it's funny that Hank is judgmental and hates who she dates. Nowadays, though, most everyone watching would hate who she dates. Many of them are 10+ years her senior and are really creepy dudes. One of Hank's best friends dating her wouldn't be a funny bit, it would be a friendship and character imploding conflict. She's an adult, but she's also a barely legal young woman with low intelligence. It's hard not to think most of the men she dated are taking advantage of her, which is really uncomfortable, not funny.
Bill and Peggy's Business
Throughout King of The Hill, Hank Hill's friend Bill shows serious signs of depression. While the show generally does well in showing his friends support him, there are a few big red flags. One of the worst things the show has done to Bill involved him and Peggy going into business together. Despite knowing his mental state, she learns that he works best under stress and actively terrorizes him to fuel their business. This is played for a joke when it's actually quite horrifying.
Though the end of the episode sets Peggy straight and she makes things better, it doesn't make up for the rest of the episode.
Cotton (And His Personality)
Hank Hill's father, Cotton, is a very unpleasant human. His rampant misogyny and dislike of his own son are played up for laughs. The show even acts like his affection for his grandson and his troubles with PTSD redeem him in some way. However, being troubled doesn't excuse awful behavior. In his first episode, he even tries to buy Bobby a hooker. Hank and Peggy saying that's wrong doesn't make up for how awful he is.
Every joke around his complicated, disrespectful personality loses a lot of their humor in a world post-#MeToo movement. Cotton Hill wouldn't pass for a complex character nowadays without some serious amendment to his brand of funny and his views on women.
Mascot Beat Down
There are a few times that Bobby gets close to Hank's dream of him being on the football team, and one of them is when he becomes the high school mascot. The only trouble is, in their town, it's customary for the other school to assault the mascot if they're losing. At his first game, the rival band started to charge him when Arlen won.
Understandably frightened, Bobby ran off. However, his family and the school expected him to take the abuse with a smile. Fans are supposed to laugh at Bobby's coward behavior and think he's brave for finally taking the beating at the end. However, modern audiences probably wouldn't find that funny. His parents encouraging him to get his teeth kicked in and feeling ashamed when he doesn't isn't quite 2019.