"Tarkin, if ever there was a shred of humanity in you or these twisted creatures of yours, it's dead now. You're at war with life itself."Named for the boundary around a black hole from which there is no escape once crossed, this trope uses the black hole as a metaphor for evil; the Moral Event Horizon refers to the first evil deed to prove a particular character to be irredeemably evil. Note the word irredeemably. It is a demonstration of permanent evil; as in, the first evil deed whose role in the story is to tell us they will always be a bad person. That moment where you know for sure that it is simply not possible wash their hands to get rid of the damned spot of blood. And of course, many villains stay evil throughout, but we're talking "If you can find it in your soul to even consider forgiving this person, there's something freakishly wrong with you." Their existence is a blight on humanity. They poison the earth they tread upon. The very air they exhale is toxic fumes. They. Are. Vile. While they may not have had a term such as this to define it, many authors clearly recognized it. Robert A. Heinlein's Stranger in a Strange Land referred to it as being the result of an act that was "so bad, so black" that it was basically unforgivable. Hank Rearden in Ayn Rand's Atlas Shrugged said that "to convict a human being of that practice was a verdict of irrevocable damnation... a verdict of total evil" and that "he would not believe it of anyone, so long as the possibility of a doubt remained." Meanwhile, multiple religions have the concept of "perdition", where those who have committed a truly unpardonable sin are irrevocably doomed to punishment in the afterlife. Obviously, it follows from the definition that a character can't cross this boundary more than once. Crossing it implies going from redeemable to irredeemable, and that's it; the other way around contradicts the definition. Of course, that doesn't mean they'll always be getting worse. Sometimes a character who has crossed the horizon will invoke I've Come Too Far afterwards... but they have still crossed the line. Yet there are ways to stem the descent into a true monstrosity. Sometimes all that stands between man and monster is a Single Tear... or even a full-out weep. Perhaps a show of respect for the enemy. A Heel Realization that you've gone too far. Sometimes they become The Atoner. But the act has been committed, and they will never fully succeed... And since it's subjective, some characters will think you've crossed it, while others may be still prepared to believe in your possible redemption. Just as with a real black hole, the closer you come to a Moral Event Horizon, the harder you must try to escape. A Complete Monster lives on the other side of the Moral Event Horizon, but crossing the Moral Event Horizon does not automatically imply that the crosser is a monster. The character can just be a bad person; the Moral Event Horizon is a black mark in their history that can never be forgiven. A character who performs an act that should make them irredeemable but somehow gets away with it is a Karma Houdini. Unless they realize it, feel horrible, and work their ass off to atone for that crossing. Then maybe it'll evolve into Forgiven, but Not Forgotten; that one crossing certainly will stay as a black mark, but they're working to be a better person. Such instances, however, are rare. Sometimes, however, there is a positive usage of a Moral Event Horizon. If in a work, a villain seems to be too ineffectual and pathetic to be a threat, yet the show wants to insist that it's a dangerous villain, letting the villain cross the Moral Event Horizon can be a good way to establish that villain's caliber, that he's meant to be opposed. In other words, it can save a supposed villain from being a failure of a villain.
— Princess Leia Organa, from the Star Wars Radio Dramas, after Grand Moff Tarkin wipes out her home planet.
- And That's Terrible: When the writers feel the need to explicitly point out when this occurs.
- Complete Monster: A possible result. However, not all people who cross it become this (although if one's become this they've definitely crossed it).
- Cop Killer: When a murderer demonstrates his lack of regard for morality by killing a representative of law and justice.
- Crosses the Line Twice: When these actions are played for laughs.
- Despair Event Horizon: A character who loses all hope can be likely to cross the Moral Event Horizon.
- Disproportionate Retribution: Sometimes, the retribution is disproportionate enough that it causes the person who committed it to cross the Moral Event Horizon, and often it does.
- Face–Heel Turn: A good guy turns bad and allies with a villain (or group of villains) and forever affiliated with same.
- Faux Affably Evil: Most Affably Evil characters can become this when they cross the Moral Event Horizon.
- Heel–Face Door-Slam: A Heel-Face turn and/or an apology is attempted, but for whatever reason(s) is rejected; in other words, it's too little, too late, and beyond.
- He Who Fights Monsters: Where seeking revenge against the villains is a way of crossing the Moral Event Horizon, in that the character will turn out to be just as bad as them.
- I've Come Too Far: When a character recognizes (or believes) that he/she has crossed the MEH and knows that he/she doesn't have a chance of redemption anymore.
- Jumping Off the Slippery Slope: A character skips over several progressively darker shades of gray and goes straight to the Moral Event Horizon.
- Karmic Death: What the irredeemable character will usually face due to crossing the Moral Event Horizon.
- Kick the Dog: An act which serves no purpose other than to mark the character as evil, which frequently overlaps with this.
- My God, What Have I Done?: The character will react with remorse after he/she crosses the Moral Event Horizon.
- Pædo Hunt: Sexual contact with a minor is treated as a Moral Event Horizon.
- Rape Is a Special Kind of Evil: Rape is easily considered a Moral Event Horizon.
- Redemption Rejection: A character rejecting an offer to redeem himself is proof that he isn't willing to turn back from the line he crossed.
- Rejected Apology: Sometimes, a character's actions cross the line to the point where he isn't forgiven for them no matter how apologetic he is.
- Slavery Is a Special Kind of Evil: Slavery is considered a Moral Event Horizon. Of course this goes first and foremost for slavedrivers who start it and not for people who are raised in a slavery-based society if they aren't cruel to the slaves.
- Slowly Slipping Into Evil: The approach to the Moral Event Horizon.
- This Is Unforgivable!: An in-universe acknowledgment that the Moral Event Horizon has been crossed.
- Tragic Villain: A character knows (or thinks) they've crossed the Moral Event Horizon, and has nothing left to do but continue to be evil.
- You Monster!: Characters will get called this, indicating that they've severely crossed the line.
- Adopt the Dog / Pet the Dog: An action by a morally neutral or ambiguous character that is meant to elicit audience sympathy for the character.
- All Crimes Are Equal: When all bad deeds, whether big or small, are equally unforgivable, although the punisher may cross it if it is taken too far.
- Easily Forgiven / Insane Forgiveness: Sometimes, acts that really should be unforgivable are shrugged off in-universe.
- Easy Road to Hell: Similar to All Crimes Are Equal, except that all crimes automatically condemn those committing them to Hell.
- Even Evil Has Standards: A villain isn't considered purely, irredeemably evil because he avoids crossing the Moral Event Horizon.
- Everyone Has Standards: Even though they may disagree on where the line is, most people believe there are lines that shouldn't be crossed.
- Felony Misdemeanor: When something that isn't really that big a deal is treated as utterly unforgivable, although the punisher may cross it if he takes it too far.
- Heel–Face Turn: In which a villain turns good.
- Heroes' Frontier Step: The good deed that shows a character will become a true hero.
- Kick the Son of a Bitch: Unlike Kick the Dog, where it's an act that marks a character as evil, this is where the act is forgivable because the one receiving it deserved it.
- Like a God to Me: Nearly the opposite of this trope. A character has done something so awesome that other characters fall over themselves to praise her/him.
- Poke the Poodle: A half-assed attempt at villainy.
- Shoot the Dog: When the hero crosses the line because it had to be done.
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- Crankshaft. The September 2013 plot arc has Crankshaft get even surlier than usual because a new co-worker is challenging his reign of smug, curmudgeonly idiot incompetence; his response is to try to 'scare' her into letting him be the festering asshole using his hard life as an excuse to be the antisocial clod he was born to be... by trying to run her over with his school bus.
- While deaths in the ring are not unheard of, they are extremely rare. So when Ox Baker killed Alberto Torres with his heart punch, that wasn't when he crossed the horizon. It was when he bragged about the death and tried to cause more with intentional heart punches that he crossed the line. And he was hated everywhere.
- Big Boss Man crossed it by killing Al Snow's dog and feeding it to him, mocking the Big Show's father's death, and stealing his father's corpse at the funeral.
- Colt Cabana crossed the event horizon in IWA Mid-South when he tried to rape Chris Hero's student, Nadia Nyce. In fact, some of his fans declare his IWA M-S run a Dork Age solely because of this incident or just choose to ignore that he was ever there.
- Jimmy Jacobs crossed the event horizon in the Independent Wrestling Association, or at least IWA Mid-south, when he appeared in rival promotion All American Wrestling and threw the IWA M-S Heavyweight Title belt in the trash. He's since shown up in IWA M-S again, in defiance of his permanent ban but is always the bad guy. He was considered a hero in AAW though, at least initially. He also crossed it in Ring of Honor when he tried to impale his ex-girlfriend the Lovely Lacey with a railroad spike, as even stablemates Tyler Blacknote and Joey Matthews felt he was going over the line.
- Brock Lesnar either crossed it when he pushed an injured Zach Gowen down the stairs, or when he assaulted Shawn Michaels and broke his arm.
- Portia Perez crossed the event horizon when she tried to kill Allison Danger's unborn child. While she had masked babyface runs prior she was never really forgiven and retired in SHIMMER with no real friends, besides maybe Matthews.
- Seth Rollins crossed it when he took a retired Edge hostage and attempted to Neck Snap him even after John Cena gave in to his demands.
- Johnathan Coachman crossed it when he punished John Cena and his father, a non-wrestler, for double-teaming Randy Orton (despite it being in both self-defense and retaliation for Orton's own (repeated) aggression against the father) by making Cena watch his father get brutalized (again) in a match with Orton. Then, when Cena understandably attacked Coachman in grief and rage, Coachman tried to strip Cena of his title as further punishment, even mocking him for foolishly rendering his father's beating pointless (Part of the stipulation was that Cena would've been stripped anyway if his father had refused to wrestle.).