Moral Event Horizon in Harry Potter.
- When Dolores Umbridge takes over, she spends most of Harry Potter and the Order of the Phoenix finding new and more creative ways to Kick the Dog (usually Harry). For her MEH, the point of no return was trying to literally torture (i.e. use the Cruciatus Curse on) Harry for information, and revealing she sent Dementors after Harry, who nearly killed for all intents and purposes an innocent bystander trying to get to him.
- Related to this, the students and teachers at Hogwarts agree with one thing: being allied to Umbridge is just as bad as being Umbridge. It gets to the point where even Snape doesn't interfere as the kids engage in good trouble to make sure the lady has an exhausting stay at Hogwarts. The only person who doesn't quite turn evil when allied with her — Rufus Scrimgeour— is also not one of the best Ministers and dies mostly unmourned (even if he does go out refusing to submit Harry's location to Voldemort under torture).
- Harry believes Fudge crossed it by setting Umbridge on the school. We have to agree with him on this one: Fudge knew exactly what kind of lady Umbridge was, and spent a whole year smearing Harry and Dumbledore rather than actually listening to them that the Dark Lord had returned. When he was forced to resign in disgrace, he had the gall to go Crossing the Burnt Bridge to ask Dumbledore to ask Harry to put in a good word for him. Dumbledore, in a case of O.O.C. Is Serious Business, didn't just say no, he told him to shove off and prevented him from contacting Harry in any way.
- In-universe, everyone at Hogwarts except Cho and the Slytherins says that Marietta Edgecombe crosses this by selling out the D.A. to Umbridge, coming willing to her office as the lady happily tells Fudge. It would be one thing if she had just sold them out at the beginning when they were meeting in the Hog's Head because that was just one meeting and wasn't illegal at the time. She waits six months, and can clearly see that the D.A. is helping Cho cope with her grief about losing Cedric, to make her move. Unsurprisingly, the students shun Marietta after learning it was her fault that Dumbledore had to leave the school after Taking the Heat for the organization, and Umbridge became headmistress. Cho tries to defend Marietta, saying it was a mistake, but Harry coldly points out that Marietta also sold Cho out, her best friend, and that is indefensible.
- Also crossed when Bellatrix, her husband, and one other Death Eater subject Alice and Frank Longbottom (Neville's parents) to a Fate Worse than Death — prolonged torture by Cruciatus curse until they became insane, unrecognizable vegetables. It's even worse than they did it after Voldemort was gone and the Longbottoms genuinely had no idea about resurrecting the Dark Lord. To rub it in that this is horrible, Bellatrix is Neville's Relative Button; he nearly tackles her, not needing his wand, when she taunts him that she's acquainted with his parents.
- Since Bellatrix's role in her torture of the Longbottoms was Adapted Out of the films, her crossing there is in Harry Potter and the Order of the Phoenix, when she kills Sirius Black and gleefully brags about it afterwards.
- Barty Crouch Jr. crosses this by killing his own father. It's ambiguous if he was guilty of torturing the Longbottoms because he claimed he was innocent and Voldemort still called him his most faithful servant — Voldemort hates traitors and those that evaded Azkaban. What's definitely not ambiguous is his glee about murdering Crouch Sr. in cold blood. Crouch Sr. was not the best father or the nicest guy, but his son killed him out of spite. Also, if he hadn't done so, Crouch Sr. would have been able to warn Dumbledore about the Dark Lord's plan.
- Wormtail is an instructive example of where true event horizons lie. While betraying Harry's parents to Voldemort, supposedly his best friends, causing an explosion that killed a dozen innocent people and pinning his mass murder on Sirius, ensuring Sirius' twelve-year psychological torture in prison was certainly evil, he could have still been redeemed. After the initial betrayal, he at least had a meager chance to start his life anew, probably in another country. But after he found Voldemort in Albania, helped restore him to full health, killed Cedric, and resurrected Voldemort, he truly cemented his place in darkness and ensured that the casualties would be much worse than those he caused himself.
- Vincent Crabbe, along with Goyle and Malfoy were mostly ineffectual rivals to our trio, but towards the end Crabbe actually almost kills the three, even when Draco is dead set against it. In the movies, due to Crabbe's actor's troubles with the law, this line crossing was given to Goyle.
- Lucius Malfoy was a willing accomplice in many of the Death Eaters' atrocities, but the moment where he slipped Tom's diary to Ginny, knowing that it would kill Muggle-born children, he proved to be capable of great vileness of his own accord.
- In the film adaptation, Harry tricks Lucius into freeing his house-elf Dobby. Lucius almost uses the Killing Curse on Harry, only for Dobby to stop him from doing so.
- Gilderoy Lockhart toward the end of Chamber of Secrets, when he tries to give the twelve-year-old Harry and Ron severe, irreversible memory damage and leave Ginny to die in order to keep secret the fact that he's a fraud.
- Bartemius Crouch Sr. crossed it (only in the novel) when he disowns his son during his trial. Even though he was (presumably) guilty, before his son did anything horrible, his son tried everything to please him countless times. Not to mention, he didn't even care about his son one bit.
- He definitely crossed it when he permanently damaged Bertha Jorkins' brain via Memory Charm. This is where you can tell that he's no better than his son.
- Snape himself is already a jerk who bullies the Gryffindor students, most notably Neville. However, the final straw is when he kills Dumbledore. Subverted in Deathly Hallows when it's revealed that it was an act of mercy since Dumbledore was dying very painfully, which Dumbledore himself arranges. Though one could argue that the abuse of innocent children already crosses the line.
- It's revealed that Grindelwald crossed it by torturing Aberforth and Arianna Dumbledore when Albus and his brother got into an argument about the two wizards' delusions of grandeur. As Aberforth was putting it at the time, you can't go on conquering the world when you have a disabled little sister at home. Arianna is killed in the crossfire, and it broke Albus. He didn't know which of them struck the killing curse, but Grindelwald didn't care. He left his best friend and lover to grieve to start his campaign. Albus, for that reason, put him in prison for life and Grindelwald spent his last moments resisting Voldemort's torture, having finally gotten a Heel Realization about why what he did was horrible.
- Voldemort may have crossed it when he tortured the children in the cave as a boy, or when he killed another boy's rabbit, or when he made his first Horcrux after killing Myrtle Warren. From the reader's perspective, he crosses it in the first scene of the series when he murders Harry's parents and then tries to kill Harry himself, a defenseless infant.
- Antonin Dolohov's murder of the Prewett brothers is this for him despite being a Minor Major Character.
- For Fenrir Greyback, his crossing is when he:
- Novels: turned Remus Lupin in a werewolf when he was four years old, condemning him to a life of painful transformations and discrimination from society.
- Films: fatally mauls Lavender Brown in the Battle of Hogwarts.
- Fantastic Beasts: Corvus Lestrange crossed it years ago by using the Imperius Curse on a married witch to have her for himself, having a child with her in what is essentially rape.
- In-Universe, creating a Horcrux is considered to be this, as it requires one to commit murder and...something horrific in order to split one's soul and keep it in another object. It's considered to be so bad that even books that go into great detail about The Dark Arts will not describe it, and it's implied that the discovering that Voldemort has created Horcruxes is what caused Regulus Black to undergo a Heel–Face Turn.
- Neville casually reveals that Alecto Carrow physically maims him when he mouths off to her. She also does it if a student refuses to use an Unforgivable Curse on a classmate for a class demonstration. Everyone else is horrified, but Neville says she'll just torture him and won't kill him because he's a "pureblood". When Luna stuns the lady, having seen her in Ravenclaw Tower to bust Harry for looking at a diadem replica, the other members of her house burst into cheers.
- Amycus Carrow plans to torture the Ravenclaw students into admitting they caused a Dark Mark false alarm having mistaken them for attacking his sister. This is so bad that Minerva refuses to abide by it and does Go Through Me saying he's not hurting a student on her watch this time. She's also more worried for Harry's conscience than for Alecto when the former tortures the man with a Cruciatus Curse, showing No Sympathy.
