The title character of Funky Winkerbean was something of a pessimist as an adult, but still mostly a nice guy. After Time Skip #2, he became a grumpy, avaricious Jerk Ass.
Played with concerning Hank Pym in the Marvel Universe. Initially presented as a Nice Guy scientist, he had a number of Jerkass moments when he became Ant-Man, particularly his tendency to dismiss and verbally put down his love interest The Wasp. However, he really took a level when he had a mental breakdown and became the anti-heroic Yellow Jacket, eventually getting to the point he tried to cause a robot attack he could foil to look heroic. After hitting rock bottom, he built up and became a Nice Guy again after some development.
Nearly every incarnation of The Hulk goes through periods where he goes from Woobie to Jerkass Woobie to just plain Jerkass. Then again, it's The Hulk. His different personalities have different levels of jerkass. The most notable one was his Grey Hulk phase, or Mr. Fixit as he called himself. This Hulk enjoyed beating people a bit too much and even accepted to work as an enforcer in Vegas so he could earn money for punching people all day. His newfound intelligence allowed him to be much crueler with his foes than the classic Green Hulk ever was. For example, when attacked by the Rock and Redeemer, he took advantage of the Rock's spinning spikes attack, smashing Redeemer against said spikes and effectively killing him.
In his earlier appearances, Curt Connors of Spider-Man was a reasonably sympathetic character when he wasn't the Lizard, and even as the Lizard retained some protective instincts towards his family. He was retconned into being Evil All Along, and as of The Gauntlet he completely lost control of the Lizard persona and killed and ate his own son. After that, his more sympathetic characterization likely won't be coming back any time soon.
The Evil All Along ret-con was pretty much ret-conned itself after the story that introduced the idea, as no other writer has used it since then.
Natalie "Envy" Adams from Scott Pilgrim Volume 3 took a several year course in jerk-assery and passed with an A+++. In college, "Nat" used to be a nerd who had a lot of anime stuff in her dorm and kept to herself. She was Julie's roommate and she ended up meeting Scott and dating him for a nice while. Her, Scott, Stephen Stills, and two insignificant others (one being Young Neil's older sister Stephanie) started a band called "Kid Chameleon" that ended up becoming pretty popular, eventually cornered by record labels. Over time, she began becoming more confident and selling her old possession for cooler things while slowly becoming more of a 'bad girl,' even using the alias Envy. However, she also ended up changing the band without the consent of Scott or really anyone with the rest of the band against the changes. In fact, it's implied that Envy may have begun cheating on Scott and certainly saw less and less value in ther relationship. Eventually, an incident at the bar led to a drunk Scott and Envy creating a large argument that Scott didn't recall anything, but Envy announced that it was over, both the band and their relation, causing heartbreak for Scott and a good deal of insecurity. Byt the time we see her in the main line, she has become pretty successful though Scott has compliations talking with her while Wallace is pissed off for what she did to Scott.Now in a band with Todd Ingram, her now boyfriend, childhood friend and Ramona's third evil ex-boyfriend, and a drummer named Lynnette Guycott. In bitter irony, Envy discovered Todd himself wasn't as loyal as she thought and with Todd's defeat and Lynette's disappearance, she was left with little else but the clothes on her back (including an old hoodie from Scott). The two didn't make closure until the final book where Envy seemed to have found success going solo, albeit being with Gideon. With his end though, not sure what happens to her, but at least the closure helped repair the damage between the two.
In The Just #1, the older heroes of Earth-16 have no issue with re-enacting major battles for fun, regardless that some of their closest friends and allies actually died in those battles. For example, they have Red Amazo (the combination of Red Tornado and Amazo) participate in the recreation of the event that actually created him, but pretty much killed the Red Tornado in the process.
Due to her Trauma Conga Line, Teen Jean Grey brainwashes Warren into submission twice! And in Battle of the Atom she manipulates Teen Scott by flattering him (after kissing Hank) to help her stay in the present, which she knows will cause an Apocalyptic Future.
After Teen Scott leaves, Kitty Pryde acts like a jerk to Modern Scott and says she doesn't want Scott and Teen Jean alone, since Teen Jean showed some attraction to Scott... even though she admits that Scott handled the situation well. Then, she berates Teen Angel for letting X-23 leave, even though there's nothing he could've done outside knocking her out, which he probably couldn't even have done.
Age of Bronze: In A Thousand Ships, Paris starts out as a slightly arrogant but relatively decent and enthusiastic youth who is a bit overwhelmed by his new life. By Betrayal, Part One, after three years as a Prince of Troy and being indulged in his behavior by Priam, he has become very arrogant, rude, pushy, and refuses to accept he could be wrong.
In Archie Comics' Sonic the Hedgehog, King Acorn in the pre-Continuity Reboot universe spiraled into this direction after the restoration of his body, disbanding the more battle-hardened Freedom Fighters to install his Secret Service and trying to force Sally into marrying Antoine, but went full tilt after his body was damaged by Antoine's Evil Counterpart Patch. Many fans were quite happy when the Reboot hit and he was back to being a generally nice guy again.
Hot Rod after becoming Rodimus in IDW's run of The Transformers. In The Transformers: Autocracy, his main concern was protecting the poor Cybertronians who lived in the slums of Nyon. By The Transformers: More Than Meets the Eye, he's become an egotistical jerk who in love with the sound of his own voice and loves being in charge even though he's a lazy slacker who pretends to be asleep whenever someone approaches him with something that bores him.
Disney Ducks Comic Universe has Huey, Dewey and Louie. One story had them complaining to each other about Donald's many flaws — only to suddenly realize that no matter if Donald is a big success or not, he still takes care of them, cooks for them, makes sure they're clothed and happy, and on the whole uses a lot more money on them than he does on himself. Cue guilt and a resolve to start appreciating their uncle a little more in the future. Later stories have them be openly ashamed on him and even come off as selfishJerkassesnote In "Where There's Smoke", one of the three said he wasn't annoyed by Donald dropping foam on them (because Donald thinks that where there's smoke, there's fire), but because he would get the badge instead of them, and the comic portrays them in the right for their It's All About Me attitude, and they even get rewarded for it instead (they get their badge at the end), and in "Paperino e i Gamberi in Salmì", Scrooge's brother Gedeon gives Huey, Dewey and Louie a stand-in of the "Pulitzer" prize, but gives it to Donald to keep it for them until they grow up. Afterwards the three are shown running Donald out of town and saying "You're not our uncle... you're a medal snatcher!" just for getting the medal, which he didn't steal it from them., and it doesn't help that they stilltake the moral high ground against Donald and win.
Near the end of his carer as Robin Tim Drake's personality took a dark turn, even using Scarecrow's fear toxin against gangsters. The reason for this was largely due to loosing his mom, dad, girlfriend, best friend, other best friend, step-mother, and adoptive father in separate instances and then having Dick, Stephanie and Cassie all betray his trust. Mostly Dick who refused to even listen to Tim's theory about what had really happened to Bruce and instead decided Tim was losing his mind culminating in Dick giving Robin to Damian, who had made repeated attempts on Tim's life.