- Ash indefinently crosses this when he sold Marceline's beloved teddy bear knowing that she loved it so much, and admits gleefully to ruining half of her life.
- Me-Mow crosses it when she poisons Jake and won't give him the antidote unless he kills Wildberry Princess and then, while talking in her sleep, she lets it slip that once Jake kills Wildberry Princess, she plans on double-crossing him and letting him die of the poison anyway.
- Ricardio crosses it when he tries to cut out Princess Bubblegum's heart with broken bottles of glass after spending most of the episode earning her trust.
- And if he didn't cross it there, he certainly did so when he tied Lady Rainicorn in a knot. At least he had a goal to accomplish with cutting out Bubblegum's heart; hurting Rainicorn was just to show off the physical strength his new body gives him.
- The Lich crosses it either when he kills Billy or when he kills Prismo, both of which were done during attempts to end all life in the universe. The latter kill is especially egregious as his victim was confused and helpless, and it's clear the Lich had no reason to kill him other than For the Evulz.
- In "Earth And Water" we learn that Flame King crossed it shortly after Flame Princess was born when he had her thrown in the forest to die just because he was somewhat worried she would usurp his thrown when she got older.
- Dr. Gross crossed it sixteen years in the past when her deranged experiments ended up accidentally causing the death of sixty-two percent of humanity on the islands — with absolutely no remorse on her part, either, as years later she's still a psychotic mad scientist who tries to hack apart Finn, Jake, and Susan for "spare parts."
- The Widow in "Min and Marty" began as a fairly sympathetic character who (justifiably) wanted revenge on Martin for selling her and the other hiders out. But she loses all sympathy once she and her goons break into his house and attempt to kill him, even though he was defenseless, with his infant son, and (seemingly) on the path to redemption.
- Warren Ampersand/The shapeshifter crossed it a long time ago when he reveals that he sucked the life force of his own children in order to extend his lifespan. And he was going to do the same thing with Jake and his kids.
- In "Come Along With Me", GOLB crosses it when he transforms some soldiers into Eldritch Monstrosities without reason and tries to destroy the Earth.
Moral Event Horizon / Adventure Time