Dragon BonesBastilla really doesn't react well to Ward rejecting her. She tries to kill him - and that even though he's really nice and respectful about it.
Nish from The Three Worlds Cycle books by Ian Irvine is eventually this for Tiaan after she rejects him numerous times.
In Death series: Indulgence In Death has a guy who killed a girl he was interested in a drunken fit of rage because she was not interested in him.
In the Warrior Cats series, Ashfur. He reacts to rejection by deciding that Squirrelflight needs to feel as much pain as he had. He tries to set up her father's death, framing her current mate as a murderer in the process. When that fails, he decides to try killing her kits in front of her.
Raggedstar wasn't good with this either. When Yellowfang (the she-cat he loved) decides to be a medicine cat, he gets angry and refuses to talk with her...and it causes him to demean and insult her a lot.
The Princess Bride: When Buttercup gives Prince Humperdink "The Reason You Suck" Speech, he throws her into her room. Then he races down to where her true love Wesley is being tortured, and sets the torture device on maximum, killing him. Clearly, the Prince did not take to being rejected by Buttercup well.
Lydia in Peter Moore's Caught In The Act towards Ethan. She gets Ethan to say he'll "stay forever" and orders him to tell her that he loves her. When he eventually tries to break up with her, she accuses Ethan of stalking her and ultimately tries to kill him using the guise of a play to stab him.
The Odyssey has Calypso who, after offering her lover Odysseus a chance to stay with her on her island forever, tries to force him to stay on her island with her after he rejects her and tries to get back to his wife at Ithica. She eventually lets him leave because Hermes told Calypso that Zeus said she had to let Odysseus go back to Ithica.
Tess of the d'Urbervilles Tess, beginning when Angel initially rejects her and she offers to kill herself, among other things, if it restores his good name.
The Sorrows of Young Werther is about an emotional young man named Werther who falls madly in love with an young woman named Lotte, who is engaged to someone else. Werther gradually becomes more emotional and less mentally stable as a result of the rejection and ultimately kills himself.
Lord Arlington in the Louisa May Alcott book The Inheritance tries to seduce Edith many times but each time she rejects him. The final time she rejects him he reacts very angrily and it's implied that he means to rape her but Lord Percy shows up and Arlington departs.
In Ellen Hopkins book "Crank" Kristina hooks up with Brendan who drives them both out into the woods, where they get high together, and he starts to take off her clothes. When she says no, he becomes violent, claiming that he has “waited weeks,” so she should “put up and shut up”. He then starts ripping her clothes off and rapes her.
In Twilight, werewolf pack leader Sam snaps, when his imprintee Emily keeps rejecting his advances. She makes it clear that she isn’t interested and sends him back to his old fiancée, Leah (her cousin). However, because San imprinted on her and is thus forced to love her even against his will, he keeps pushing her. Finally Emily calls him out on being just like his father (who left his family), unknowingly pressing Sam’s Berserk Button. Thanks to a mix of frustration over her rejection and his daddy issues he attacks her in his wolf form, scarring her for life. And then they lived happily ever after!]] (...No, seriously—she just found out he was imprinted on her and decided she would just go along with it.
It's also hinted that Edward, due to how controlling he is over Bella, would not take it well if she ever rejected him or left him.
Bella herself effectively went catatonic when Edward broke up with her. The infamous blank pages showed that well enough. She proceeded to spend most of the book finding various self-destructive ways to hallucinate Edwards voice.
Jacob threatens to kill himself when Bella pays more attention to Edward, but Edward says it's just a ploy to get Bella to kiss him.
Both Christian Grey and Ana Steele in Fifty Shades of Grey. Grey breaks into her duplex and rapes her into submission when he receives a rejection email; when Grey refuses to kiss Ana, this is her response:
Once underneath the dark, cold concrete of the garage with its bleak fluorescent light, I lean against the wall and put my head in my hands. What was I thinking? Unbidden and unwelcome tears pool in my eyes. Why am I crying? I sink to the ground, angry at myself for this senseless reaction. Drawing up my knees, I fold in on myself. I want to make myself as small as possible. Perhaps this nonsensical pain will be smaller the smaller I am.
The Mortal Instruments: Really, it gets to the point where should-be True Companions are abandoning each other to vampires and demons for slights like "I can't believe you like her/him more than me!" and "It wasn't my fault!" Kind of sends the underlying message that this is all teens are capable of.
In Best Served Cold, Caul Shivers risks his life to save Monzcarro's many times, even being permanently disfigured on her behalf. After the last such attempt, she has a tryst with the Grand Duke Rogont...and Shivers decides that he's now ready to kill the woman he's saved half a dozen times.
In Lisa Scottoline's book Every Fifteen Minutes Kristine makes flirtatious advances towards Eric who rejects her. In response she files a sexual harassment claim against him. Subverted in that she later makes peace with him.
Laurie however is revealed to be a sociopath who manipulates and sleeps with Sam in a grand scheme that results in people dying because she's angry that Eric chose Caitlin over her. She also threatens to Blackmail Eric while brandishing scissors. When Eric finds out about her ruse and she realizes she can't have him she grabs scissors and deliberately cuts herself with him. In her mad delusion she informs him that she's going to tell the cops who are on their way that Eric tried to date rape her after she drank too much. She says she'll tell them that when she resisted his attempts to rape her he grabbed the scissors and held it to her throat. She then says she got the scissors from him and tried to run but Eric tackled her before ripping her shirt open. She says she had to kill him because it was self defense. She then makes good on her lie by advancing on him while similtaneously ripping her shirt open and attempting to stab him with them but he manages to stop her.
In Evan Roskos book "Dr Birds Advice For Sad Poets" after Derek breaks off his fling with Sally she throws a tantrum, vandalizes his front lawn, throws homophobic slurs at James, and threatens to get her fiancé involved.
Amy in Gone Girl wants to get her revenge on husband Nick for cheating and not paying enough attention to her by framing him. When she comes back after Nick promises to be a better husband she threatens to do terrible things to him again if he tries to leave her.
Desi was rejected by Amy back in college and has since stalked her and tried to keep her isolated in his cabin to keep her safe against her wishes.
The Dagger and the Coin: Geder is not good with rejection. How not good? He sends an army to invade Birancour because Cithrin, who rejected him, is living there, to capture her and bring her back in chains.
After being rejected by Harry when he offers him friendship, Draco spends their first year trying to thwart Harry, and apparently complained about him through the entire summer break, and in their second year he's so busy teasing Harry that he completely misses the Snitch and loses his first game. Moreover, he's always doing things to get his attention in the Great Hall, even though the Slytherin and Gryffindor tables are on opposite sides and have the two other houses between them. Apparently, Draco has been frustrated for over seven years, because he teased and bullied Harry at every opportunity he got, since their first encounter. He was so deranged by Harry's refusal, that he became his greatest rival. Too many issues, Draco?
This trope is also part of Bloody Baron's backstory. When he was alive, he found the woman he loved (whom Rowena Ravenclaw tasked him to bring back to her after leaving her). He killed the woman in a fit of rage after she rejected him, and then killed himselfafter realizing what he had done. Both of them returned as ghosts and have remained in Hogwarts since then.