All in the Family: Mike Stivic apparently turned into a jerkass after he, Gloria and Jr. moved to California. We never see exactly how it happened, but he started to ignore his once beloved wife and son, slept around with another woman, compared marriage to Hell and called Gloria fat.
Arrested Development: Happens to Michael and, to a lesser extent, George-Michael, in the fourth season. Michael becomes desperate and petty in his attempts to get his family's permissions for his movie and dating Rebel Alley, and has a falling-out with his son. George-Michael, meanwhile, takes center stage in his own personal Fawlty Towers Plot.
Penny and Leonard to some extent. Penny started off as a quirky-if-emotional Na´ve Everygirl who developed into a butch, cynical alcoholic, while Leonard became a bitter jerk, though that at least depended on the writer.
Priya and Raj in season four. For Priya, she basically forbade Leonard and Penny to hang out together due to jealousy, then she lies to Leonard about not moving back to India. For no adequate reason. Karma Houdini doesn't cover it. For Raj, he begun to have lust for Howard's fiance Bernadette (and when being told a rumor of them breaking up, wanted to date her even though Howard possibly wouldn't let that fly) and then after Penny falling asleep before they could have drunken sex still acted like an ass that slept with her.
Boy Meets World: Jack Hunter in season 7. He started out basically a Nice Guy who was a little naive due to being new in town and occasionally exasperated with Eric's Cloud Cuckoo Landerness. In the season 5 premiere episode "Brothers," we are introduced to him as someone raised by an upper-class stepfather. His estranged brother Shawn assumes he's a rich brat because of this. However, in the following episode "Boy Meets Real World," while he and Shawn are arguing, Jack admits to working summer jobs in order to obtain the money he has, thus giving Shawn and the viewers a positive impression of him. But he seemed to transform into a Jerk Ass after his breakup with Rachel in the season 7 premiere episode "Show Me the Love." Throughout season 7, he degrades into a narcissistic, spoiled pretty-boy. This is especially lampshaded in the ante-penultimate episode "Angela's Ashes," when Jack is cut off from his father's funding. Rachel tells him he can't go to fancy restaurants, shop at name-brand stores, get expensive haircuts, and such. Jack whines throughout the episode about this, even as he's saying goodbye to Angela who's leaving for Europe for a year with her Dad.
She had become increasingly arrogant over the last two seasons. It's partially justified in that being yanked out of Heaven and coming to Buried Alive in her own grave had been very traumatic. However, by the last season she had practically declared herself dictator of the group and made unkind comments when one of the girls under her charge committed suicide. She got voted out of the house a la Big Brother.
This is hardly the first time she does. First she is stressing over The Master, and her Jerkassness as he starts to affect her would impress Faith. Later everyone took a level after she runs at the end of the second season. Justified in the fourth season as a demon was stealing her soul. And in season five a magical retcon gives her a sister, and Buffy struggles with this. In her second (and final) appearance in Angel, she also acts like a total jerk, doing a temporary Face-Heel Turn and trying to kill Faith, willing to fight all the good guys just to do so, then flipping Angel off verbally before she returns home.
Speaking of Faith, she does this to a frightening degree after she accidentally kills someone, to the point where Buffy is happy to kill her. She gets better following her first Angel appearance, however, to the point that she's one of the nicer characters by the end of the television series.
Speaking of Angel, Wesley inverted it before taking a higher level that went side by side when he increased his badass levels. On Buffy he was a pompous, smug jerk that everybody found to be a pain in the ass, but after he was fired from the Watcher's council and moved over to Angel he'd taken a slice of humble pie and became far more sympathetic. Then season three came and put him through the emotional wringer. After that, the same generally nice guy from the first two seasons ruthlessly stabs a harmless junkie at one point in order to make her reveal what she knows about Angelus. And tying in with Faith cooling down from her own Jerkiness levels, she actually winds up being horrified at his actions.
Riley Finn tries to make himself Darker and Edgier in an effort to appeal to Buffy in Season 5. It doesn't end well.
Buffy's dad was initially portrayed as a good guy who just couldn't see his daughter as much as they would've liked because they lived so far apart. A few seasons later, he's portrayed as a deadbeat who won't visit his daughters even when their mom dies, and Buffy believes the reason he and her mom split is because he cheated on her. Because good parents make boring television.
Charmed: Phoebe seemed to take a level in jerkass at the end of her relationship with Cole.
Chuck: In Season 5, Morgan, the title character's friend, turned into quite a self-entitled asshole, brushing off Chuck and the rest of his team, and even going as far as joining a rival spy firm. However, Morgan himself isn't at fault for it, as the Intersect that he gained at the end of last season was "tainted", causing him to lose himself, so to speak. He eventually had it removed after four episodes or so.
Community: Pierce and Abed respectively went through this in the second and third seasons. Pierce started out as a fairly harmless Cloud Cuckoo Lander who eventually, after feeling his friends will leave him eventually, turns into a total Jerk Ass who goes so far as to try and egg on a suicidal student. Abed wound up embracing his dark side over the course of the third season which saw him regularly insult his friends and often do whatever he wanted regardless of any of their feelings. However, while Pierce does become a bigger jerk, he also became more sympathetic and developed a Freudian Excuse, making him an odd combination of this and Took a Level in Kindness. But the most extreme example is Chang, who went from an annoying teacher to an insane murderer.
Criminal Minds: Season 1 serial killer Karl Arnold is shown again in season 5 episode "Outfoxed". Sure he wasn't a nice guy when they caught him, but four years later, he's got even worse.
We've seen this happen a few times as various crewmembers' clout increase, especially in season 6:
The Northwestern's resident Woobie/Determinator, Jake Anderson, wanted to go to the captain's chair after his climb up the crew ranks at the beginning of the season, prompting Captain Sig Hansen to swap him for a few weeks with Jake Harris of the Cornelia Marie, who was reaching a boiling point with his elder brother Josh.
However, in season 7, when Jake is being taught how to be a captain by Sig, even allowed to run his own string of crap pots, he shows surprising humility. When his string comes up almost blank, he blames himself more than anyone on the crew and resolves to work harder to make up for it. A distinct example of losing a level in Jerkass.
Inverted Trope on the Time Bandit, where the other crew started treating Mike Fourtner badly when he was actually given a test run in the Captain's chair.
And then there's Freddy Maughtai when he joined the Wizard, especially in Season 9 when he led the bullying of a greenhorn. It got so out of hand, some fans are demanding the ship's dismissal from future seasons.
Dexter: Detective Quinn in season six. He had already stolen from a crime scene earlier in the show, but he got worse. After screwing up at work he shows up to his ex-girlfriend/new boss Debra's housewarming party drunk off his ass with a girl he picked up from a bar, and proceeds to act like a douche to all present. It's quite telling that even the girl leaves because he took her to his ex's party simply as a cheap insult, and his partner (Batista) straight-up slugs him when he takes it too far by harassing his sister. In the following episodes he goes out drinking on week nights, behaves like an obnoxious asshole at strip clubs, doesn't show up for work, gets his partner almost killed by getting drunk and sleeping in instead of going to work. When he's fired for it, he manages to stay by exploiting a loophole intended for helping alcoholics. (He is an alcoholic, but only because he's such a Jerkass, not because he actually needs help)
The Daleks. The original race in the first Dalek serial are, in addition to being very wimpy and dependent on special floors for transport, are radiation Mutants - rather pathetic, semi-sympathetic creatures that only really care about their own survival, although, due to having become dependent on radiation to survive, ensuring this also ensures the murder of ordinary people of Skaro. They remain racist and do a bit of Putting on the Reich, but in a rather more toned-down manner than, say, a billion billion Daleks attempting to commit genocide against everything else in the universe. They also do not roll around yelling their later Catch Phrase, "EXTERMINATE", the whole time - one merely says that "they are to be exterminated - you understand, exterminated", which of course was Flanderized significantly into the point where wonton exterminating becomes their raison d'etre. This is generally all agreed upon to be a huge improvement, though.
Everybody Loves Raymond: Debra started out in the early seasons as a fairly reasonable everywoman who seemed to have a quite playful and loving relationship with Ray. Then, the character suddenly changed. It's hard to pinpoint exactly when the change occurred, but Debra eventually became a raging, physically-abusive and smugKarma Houdini who treated Ray like trash, beat him up, forbade him from seeing his friends most of the time, and convinced Ray's own children to feel contempt for him. Oh, and the worst part? The show tried to act like she was the reasonable one, despite her abusive, Jerkass behavior. So basically, she went from being a well-rounded, likable character in the beginning to the writers' Mary Sue by the end.
Farscape: Chiana is a lot angrier and bitchier in Season 4 than was in previous seasons. This can be explained by her truly horrible experiences between Season 3 and 4, when she was being tortured and raped.
A mild example, but the Frasier in Boston was nowhere near as elitist and snobby as the Frasier in Seattle. He's still basically good, but his shell of superiority is a bit thicker.
Phoebe, way more so. She becomes increasingly more shrill and mean-spirited as the seasons went on.
The whole gang towards Ross during the post-Emily debacle. The guy's just had his second marriage implode, another love of his life disappear and is slowly having a complete and utter mental breakdown, culminating when he screams at his boss for stealing a sandwich!. And none of his friends seem to notice or care, but instead repeatedly mock him about it!
Finn Hudson recently cranked it up a notch. After whining about being cheated on by his last two girlfriends, he eagerly began an affair with one of them while she was still in a relationship with Sam Evans.
Sebastian Smythe is another example. Sure, he was always a jerk, but mostly in the "lovable rogue" sort of way. Some people even shipped him with Blaine or Kurt or both. Fewer people do now thanks to him tampering the slushy, causing Blaine to need surgery.
Becky was a sweet kid in Season one but under Sue Sylvester's influence became mean and cruel.
Artie has shown signs of this in Season 3, especially when he's playing director.
Vanessa and Jenny. Jenny gains points for having gone from sweetheart-everyone-adores to being hated by pretty much all of the NJBC.
Blair Waldorf was never a nice person per se but even many of her devoted fans had enough of her by season five. She treats her fiancÚ horribly yet somehow feels he is the bad guy for not putting up with all of her whims (including briefly running off with her ex-boyfriend Chuck and professing her eternal love for Chuck minutes before the wedding). She claims to love Chuck but treats him like dirt under her shoe. She spends several episodes trying to help her best friend Serena win back Dan, then turns around and begins to date Dan herself (while still married), making out with him in Chuck's bedroom and right in front of Serena moments after Serena's grandmother died, even though she doesn't have romantic feelings for Dan. Then there's the fact that she treats Dan with little to no respect while they're supposedly friends or while they're dating. And let's not forget that she doesn't care that her own baby died but she's terribly depressed that when her two month old marriage to the prince ends she no longer gets to be a princess.
Dan Humphrey is the prime example from Gossip Girl. He started out as the show's moral compass who always believed in doing the right thing. Flash forward to season three where he's dating his lifelong best friend Vanessa but cheats on her with Serena (who, at the time, was dating Dan's only male friend Nate) and doesn't seem to think he's done anything wrong. When Vanessa for some reason wants to get back together in season four he begins to sleep with her and lets her think they're back together, leaving her to take care of the son he has by Georgina Sparks while he runs after Serena. By season five he has fallen in love with Blair and could care less that she drove his sister Jenny out of town. He then publicly humiliates Blair at her wedding by sending in a video to Gossip Girl which he blames first Chuck and then Serena for. He then tells a newlywed Blair that unless she begins to date him (Dan) he will no longer be her friend. They do date for a while but then he cheats on her with Serena. When he finds out Blair is leaving him for Chuck he makes good on his promise to not be her friend unless he can be her boyfriend and sets out to write a book that will uncover all her secrets (and the secrets of the rest of the NJBC) because he feels wronged. So much for moral compass....
Homicide: Life on the Street: Kellerman in the later seasons, for (arguably) understandable reasons in response to certain plot developments.
House: Dr. Eric Foreman, who started off as a fairly self-possessed guy who didn't really appreciate House's shenanigans, and then progressed to the type of guy who screwed over a colleague and then stabbed her with a dirty needle (the latter under duress, but still). His jerkassery has calmed somewhat, but hasn't completely gone away. To be fair, the growing jerkassery did become a plotpoint after that — Foreman was afraid that spending so much time around House was causing him to become more like him. He quit Princeton-Plainsboro to try to stop this... but then got fired from a job in New York after using very House-like tactics. Cuddy even once called him "House-Lite." Meanwhile, House's own jerkassery grew out of control as the show went on.
In the second season, Nina went from being a mostly friendly, brave friend to constantly snapping at her friends, even though they were trying to help her. She does have slight justification, though- she was under a ton of stress at the time, and was noticeably nicer when the life of she, her friends, and her Grandmother, weren't on the line.
Something similar happened to Fabian around the third season, albeit to a lesser degree. Having gotten over his Extreme Doormat phase, he got rather aggressive, to the point where he gave Joy an overly harsh rejection and caused her to quit Sibuna. He became MUCH worse as a sinner.
Joy had one too in the second season. In the first season, she was only seen for about four episodes, but was helpful and kind and was a bit of a woobie. In the second season, when she moved back into the house and joined the main cast, she was always trying to date Fabian despite knowing Nina liked him. Bad enough, but then she decided to write an anonymous article in the school paper which was basically a "The Reason Nina Sucks Speech". To make things worse, she then turned on Mara and Patricia, who were the only ones still willing to be her friend. Thank goodness she redeemed herself in the end, because it's a bit obvious why she became The Scrappy for a lot of fans.
Not even Mara was safe from this- in fact, her first time was in the middle of the first season, when she was angry at Mick calling her boring and re-invented herself for a few days, becoming much ruder and more careless. She also tried to expel him. In the third season, though, it was Jerome cheating on her that made her grow into a jerkass, doing whatever she can to get revenge on him. It was fine at first, but then she decided to have Joy pretend to fall in love with him, then break his heart in front of the school. After finding out Joy really did fall for Jerome, she flipped, and turned on her. Only in the end did she calm down and become a better friend. However, this was somewhat justified, as she still had feelings for Jerome and was really heartbroken, and felt betrayed by Joy.
Heck, Jerome cheating on her in the first place counts too.
In Season 6, Zoey Morrison gets Ted's entire class to do this when he tells of his wanting to tear down the Arcadian.
Barney does one in season 5 after breaking up with Robin (which is saying something, as he already was a pretty big Jerkass, albeit one with a Hidden Heart of Gold). He goes back down to his pre-Robin level of jerkery in season 6 though.
Sam was a bully from episode 1, but she takes level after level. A couple of her points include the episode she bashed Freddie with a tennis racquet and chucked him out of a treehouse for a differing opinion, and then later starting a basement sweatshop using elementary school kids to mass produce their Penny Tee Shirts.
Freddie takes a level in "iCan't Take It", while he is dating Sam, he edits Carly out of a webshow skit (something he never did even to Sam when they hated each other), and taunts her about being jealous of their relationship.
Merlin: Morgana. She always was rebellious and butting heads with Uther, but it was because she didn't like his treatment of magic users and was upset with the rumors of him offing the man she thought was her father. But, after she found out Uther was really her father and had lied she went full on evil. Even when Arthur became king (after she had Uther killed), she didn't stop because she views Arthur as being just like Uther and believes only she can bring back magic. Still, she's more evil than anything else now.
Merlin. He started out as the ultimate Nice Guy, but after a long, extensive Trauma Conga Line over the course of five seasons and his inability to talk to anyone about his problems (both because only his Secret Keeper knows about them, and his psychological hangups toward admitting his faults), Reality Ensues.
The O.C.: Seth Cohen becomes noticeably more self-absorbed in later episodes. Arguably this helped round out his character a bit more and explain his previously inexplicable unpopularity.
Ryan was one of the more likable and sympathetic characters in the first few seasons, but his sudden rise to power at Dunder-Mifflin coincided with a massive increase in the size of his ego. His humiliating, highly public fall from grace only seemed to make things worse.
This also seems to have happened with Pam, albeit to a lesser extent.
Andy presents an Inverted Trope — originally Jim's new foil (or "Dwight 2") when he transfers to the Stamford office, Andy has become the "all-around nice guy" in Scranton following anger management courses and (more likely) Executive Meddling to avoid having two Dwights.
Andy later plays this trope straight in the final season, where he's portrayed as an incompetent Jerk Ass who doesn't respect his girlfriend. This is mostly done to justify having Dwight take over as the new boss during the Grand Finale.
Power Rangers Time Force: Alex seems like a nice guy prior to being Not Quite Dead. When he appears later in the series, he's turned into a cold jerk who doesn't listen to anyone else. This could be due to his near death experience, possible changes in the timeline, an obsession with protecting said timeline, or any combination of the above.
Played with to the point of Zig-Zagging Trope with Charlie Matheson. The episode "Sex and Drugs" had her really tearing Aaron a new one, and agreeing to help a drug lord murder a man over burned poppy fields. In fact, Miles Matheson was the one who had to stop her from going through with it. Her Jerkass tendencies pop up every now and then after that, but it's due to Depending on the Writer.
Rachel Matheson. After she got rescued in episode 10 and watched her son Danny die in episode 11, her attitude takes a turn for the worse. She slapped Charlie when her daughter tried to call her out on abandoning her and her family all those years ago in episode 12. In episode 13, she knocks out a rebel and was going to kill Tom Neville before Charlie convinced her not to. In episode 17, she knocks out Lee Blackmore and tells Aaron to run with her. She reveals that her son's death is more important to her than the death of Blackmore's son, and that she wants to turn the power on not to help everyone, but so that the other territories will have the power to kill Monroe... and avenge Danny's death in a sense. She threatens to abandon Aaron...and this was after he went to so much trouble to not abandon her and save her life, which occurred because she screwed up. Sure, losing a son is a terrible loss, but when everyone else is pointing out the problems with her reasoning and making more sense than she is, that's quite telling.
Roseanne: The titular character started out as a gruff, but otherwise friendly and wisecracking blue-collar woman who loved her husband and kids, and slowly transformed into a cruel, selfish, sniping, raging, shrieking bitch with severe misandrist tendencies. On top of that, she was often portrayed as being in the right and getting away with being an asshole to everyone. Her daughter, Darlene, seemed to follow her into this mold. Given that this dovetailed with the men of the show (particularly Leon, Mark and David) becoming more and more pathetic, useless, and stupid, and that the show was practically written and run by Roseanne herself, it's a pretty clarifying look into her mindset at the time.
Six Feet Under: Nate, even though the personality changes are very gradual and subtle. His idealistic, free-spirited nature doesn't mesh well with his family responsibilities in season 5. Similarly, Rico.
Chloe takes a few levels in the latter seasons. Her husband Jimmy had evidence that Davis was a psychotic serial killer, and not only does Chloe refuse to give Jimmy the benefit of the doubt, but it becomes blatantly obvious that she indeed does harbor romantic/sexual feelings for Davis, despite having just married Jimmy. So from Jimmy's perspective, not only does his wife refuse to believe his warnings that this other guy is a murderous psycho, it becomes blatantly obvious that she's been (and continues to be) lusting after this other man. Jimmy was put in a nightmarish situation that broke his heart and left him isolated. His friends all treat him like he's gone crazy (even though it turns out that Jimmy was actually right about everything) and Chloe isn't there for him. His dumping Chloe was thus completely understandable and warranted. Then in Season 9, after Jimmy and Davis are both killed as the culmination of the aforementioned situation, Chloe decides to go Big Sister Is Watching on everyone (including monitoring Clark and Oliver's phone calls and emails, even setting up hidden cameras at the Kent farm), putting Oliver in a series of life and death "games", stealing money from Oliver when she could have just asked to make kryptonite weapons, and more.
Cody Martin has been known for most of the franchise as socially-awkward but lovable nerd. One couldn't help but root for him in the first season of On Deck as he fought with painstaking care to win Bailey's heart. Then, in the second season, he suddenly became full of himself, constantly fought with Bailey for dominance in the relationship, and even assumed Bailey and former love-interest Jessica were jealous of one another, despite a complete lack of evidence thereto.
When he and Bailey broke up and Zack got a girlfriend, after which he starts making fun of Zack for having a girlfriend, and gains the sexist attitude that Zack recently got rid of. It gets to the point where the viewer can't blame Zack for almost wailing on him in "Love and War".
The reserved, geeky, empathetic young Sam Winchester fans loved in Seasons 1-3 is pretty much gone nowadays, leaving a humorless, angry, unsympathetic (both towards other characters and for the audience) replacement in his wake. He first really took a level in jerkass in Season 4 due to his arrogance and low opinion of Dean rearing its ugly head thanks to Ruby and his addiction to her equally-corruptive demon blood, but even then, you got the sense that he was trying to protect Dean in his own way (he believed that Dean had been broken in Hell) and was doing all he thought he could to save the world from Lilith, and he got taken down that level in jerkass in the fifth season when he realized the error of his ways. He took one again in the first half of Season 6, but only because he was soulless, his soul still being tortured in the Cage by Lucifer and Michael—when the situation was resolved, he pretty much went back to normal. He only really turned into an insufferably selfish Jerkass under Jeremy Carver's reign as showrunner in Seasons 8 and 9. In Season 8, he abandoned not only his brother and their friend to Purgatory without looking into what happened to them (arguably understandable, since they appeared to have exploded along with the Big Bad and Sam was not in best frame of mind, having only recovered from his PTSD-induced Sanity Slippage a mere five episodes ago—though fans have also pointed out that that's never stopped him before in similar circumstances), he also knowingly left the teenager Kevin to the demon Crowley's clutches and didn't even bother checking his phones to see if anyone—Dean, Castiel, Kevin, or anyone else—was trying to contact him. His family and friends had to save themselves while Sam hooked up with a universally-loathedJerkass and slept with her behind the back of her much more likeable veteran husband even after they found out he wasn't dead after all (she must've been a bad influence on Sam). When Dean does return, Sam seems less enthusiastic than he usually does in their reunions and actually seems annoyed that his brother had the nerve to not be dead and gone. Sam then spends over half of the season hating the guy who did save Dean—a Friendly Neighborhood Vampire named Benny—and insisting that he couldn't be trusted and they should kill him, in stark contrast to his previous sympathetic response to non-malevolent monsters (he was even usually the one who had to stop Dean from killing non-humans on principle!). The explanation given at the end of the season for this is that Sam felt guilty over not having been there for Dean himself, but not only did this come literally in the last episode of the season (giving people no reason to feel sympathy until then), he comes off as such an A-hole towards Dean and Benny (who ends up not only losing his support-system and suffering on his own for months because of Sam's persecution but even willingly letting Dean kill him to save Sam because he knows how much Dean cares about his brother) before that that it's hard to justify it. Fans start off Season 9 being upset at Dean on Sam's behalf for going against Sam's express wishes by keeping him alive by helping an angel possess him through trickery, but Sam's reaction to finding out about it (he essentially told Dean that they shouldn't consider themselves brothers anymore—when their bond has been the heart of the show since the get-go—and that Dean only did things when he didn't have to pay the price, when poor Dean not only values him and their bond above all else but also is frequently paying the price for not only his actions but also everybody else's, Sam's included) was so cold-hearted that they completely switched sides, supporting Dean while being upset at Sam. There's no feeling that Sam cares about Dean (or anyone other than himself, for that matter) anymore. Many fans are disillusioned with him and the brotherly bond in general right now and are really missing the earlier seasons, but the writers seem blind to all of this, maintaining that all Sam's actions are signs of growing maturity. It essentially boils down to Sam being Unintentionally Unsympathetic and Dean being Unintentionally Sympathetic.
Two and a Half Men: Alan started off as a down on his luck man whose wife threw him out and took him for everything he had, his brother and mother are narcissistic assholes and his son became a moron over time. But in later seasons, Alan became a sleazy weasel who refuses to pay for anything and made his brother pay for everything until he was pushed in front of a train in Paris. And yet he makes himself out to be a Nice Guy and the Only Sane Man. Made even worse in the most recent seasons, where it's increasingly obvious he's being a parasite towards Walden, and in a several episode arc even pretends to be sick to mooch more from Walden, as well as his family and friends.
Jade West in the second season. In the fourth episode, she sabotages Tori in an effort to steal a role in a musical by forcing her to repeatedly donate blood Robbie needs for surgery, and in the fifth episode, she attempts to wreck the prom Tori created because Tori unwittingly held it on the same night as the one-man show Jade was planning. Possibly justified by the fact that Beck, who usually calms her evil side, hasn't been around as much this season.
To be fair, since the main cast are portrayed as being either sophomores or juniors in high school, what reason does Tori have for even wanting a prom when it wasn't her time? Not that it excuses Jade being Jade, but Tori more or less ruined Jade's big night.
Similar to the above is the story of Justin Russo. Justin was originally just a lovable nerd whose over-achieving sometimes got the better of him, and later on a badass who would fight to the death for his loved ones. Following the "Wizards vs. Werewolves" special, Justin became his sister Alex's bitter arch-rival.
The three siblings in the finale, temporarily. They soften up towards each other once they work together to bring business to the sub shop.