- If taken to extremes, it can result in a case of Ron the Death Eater.
- In Keepers of the Elements, Courtney starts off as her usual bossy, Jerkass self, but then goes up Over Nine Thousand levels when she makes a deal with Radcliffe for powers of her own so she can get revenge on Gwen.
- The Child of Love: The more hurt and more distraught Asuka feels the harsher her temper gets and the harder she tries to push everyone away. After finding out she got pregnant she was shattered, so her behaviour became very angry, rude and overbearing, especially to Shinji whom she tried to push away as hard as she could precisely because he was the one could get through her.
- The One I Love Is: Shinji. Several times. When Asuka tried -clumsily- to seduce him he thought -for absolutely NO reason- she was just trying to screw Rei, so that he slapped her, called her names and treated her like dirt during several days. Later he insulted Rei and made her crying because she had not told him who was the Fourth Child. In his defense, he later admitted he behaved like an ass and apologized to both girls.
- In the Disgaea fanfic Disgaea: Jewel of the gods Laharl is a HUGE Jerkass to Adell, and Mao not even caring if they died, while in canon, he has a Hidden Heart of Gold for people.
- Well to be fair, Flonne isn't there most of the time, making him a complete asshole to most people.
- He also REALLY hates Adell and Mao for being main characters in the sequels to Disgaea.
- In Herding Cats, Tavros of all people becomes a huge dick after being successfully shipped, particularly towards Equius, Sollux and especially Aradia to the point where the two of them become kismeses. It happens as a result of his becoming Vriska's moirail, because she helped him become confident enough to overcome his own problems and be more assertive, but neither realised how over the top he was being. Everybody else has to point out that there's a difference between countering light insults from others and being absolutely horrible to them. They also have to point out that anyone who does something as horrible as blaming Aradia for his spine getting broken and tries to play it off as being assertive seriously needs a reality check. He gets put through the wringer for it.
- This actually happens to more than a few people. After Eridan and Terezi get together, Karkat flips his shit and goes off on an angry rampage that lasts for most of the fic. In turn, Terezi continually throws horrible barbs at him, coming off as a huge bitch herself. Later, Tavros rubs off on Gamzee, who continually treats Equius like shit.
- Sherlock Holmes in Children of Time: the series is really about his development as a person, from good to better to worse to worst to best. Yes, really. And after having seen him as a lighter, happier Holmes early on in the series, it's really tear-jerking to watch that lighthearted-ness break down until he's outright emotionally abusing the Kid Hero of the story. And it only gets worse from there.
- Moonpaw in the Warrior Cats fanfic, Moonlit Path Disloya L Hearts. She starts out spunky with a bit of sass. Later on, she becomes a selfish jerk. Her sudden dip in niceness is more understandable when you consider that she started going bad right after she receives a dream predicting her death.
- As Sayu points out in The Faceless: "Everyone used to love my brother. Now, he is a complete asshole."
- The now adult Takeru in the Tamers Forever Series is much more blunt and cynical than he was as a child. The fact he used to hold the Crest of Hope makes this darkly ironic no less.
- Maylu from MegaMan NT Warrior fanfic, Maylu's Revenge, has become like this, lashing out at Roll for making her unable to continue in the N1 Grand Prix after turning her back to normal from being Empress, and not being able to become a strong NetBattler. This would lead her into defecting to World Three and attempting to delete Roll as revenge for the moment.
- In the story Sylvia the Sylveon, Alseides and Vapor, two of Sylvia's brothers, the former due to the disappearances of two of his other brothers (both of whom, coincidentally, Took a Level in Kindness) and later, the illegal fighting for which he is trained after he himself is kidnapped, and the latter due to both being mistreated by his trainer and not getting the evolution he wants.
- Navarone becomes increasingly unpleasant over the course of Diaries of a Madman, though this is acknowledged in-universe and also justified due to the bad stuff that happens to him over the course of the story. However, he does improve on this in a few areas as well.
- Neville becomes more and more of a Jerk Ass Stu as Dumbledore's Army and the Year of Darkness goes on. Mostly this is due to the fact that he starts to see himself as a military leader and begins to expect military discipline from his underlings, while the said underlings still see him as their fellow classmate.
- This happens in some Harry/Ginny fics, which emphasize Harry and Ginny's relationship, in part, by playing this trope straight with Ron and Hermione, despite the fact that both Ron and Hermione supported Harry/Ginny in canon. Particularly seen in the works of sbmcneil and Epeefencer, to the extent that Ron can sometimes border on Ron the Death Eater, and Hermione could greatly benefit from sensitivity training — from canon!Ron.
- Prototype: Equestria Strains has Pinkie Pie. She tries to hide it under her normally happy self, but it's clear the stress caused by the outbreak and losing her friends is taking its toll on her.
- Chrono Reflect has Standard Fluttershy. This is justified, though: After her best friend and sworn protector Rarity dies, she's left with no one to save her from her bullies. This forces her to stand up to her bullies, but she lets her drive to never be weak again take things to far and she ends up being the biggest bully of Canterlot High herself. Fortunately Forest Fluttershy forces her to take a level in kindness after beating her, and she starts being nice again. ...Somewhat.
- In Love the One You're With Vanessa callously dismissed Gretchen as a step down for Ferb, effectively ensuring his crush on her is long gone.
- Snotlout in oh so many How To Train Your Dragon fanfictions. Likely because they mix his portrayal from the books with one from the movie/show (many also add book characters such as Camicazi, Thuggory etc.). Alvin the Treacherous also gets hit with that, and for same reason, though for a much lesser extent.
- Carol Danvers from A Prize For Three Empires. Due to the level of trauma suffered, coupled with a gradual power loss, Carol becomes angrier, more mean-spirited and more unpleasant until a talk with her mother makes her realize that she is just making things worse for herself.
Took A Level In Jerkass / Fan Fiction