Practically every primary villain in the series has crossed it one way or the other.
- Akihiko Kayaba traps 50,000 people in the titular VR MMO, making it so that death in-game will cause the death of the player in the real world as well. They remain trapped for two years, during which time thousands of people die. If that weren't enough, he inserts himself into the game in the guise of a heroic player, leading the game's biggest guild, with every intention of betraying the other players in the future and becoming the "final boss" purely to create more drama. His reason, as best anyone can figure out from what's explained, was to try and make the world of his imagination as real as possible. Kayaba is an odd case in that the source material depicts him as ultimately sympathetic, but most of the fanbase disagrees.
- When the players are freed from SAO, Nobuyuki Sugou manages to trap over 300 of them in a game of his own in order to run mind control experiments on them. If that weren't bad enough, he also traps Asuna and convinces her father to let him "marry" her while she's still in a coma, gloating to Kirito that Mr. Yuuki doesn't realize that Asuna would never consent to it if she were conscious. He comes very close to raping Asuna in front of Kirito, then made a vicious attempt on Kazuto's life IRL, and unlike with Kayaba it's clear that nobody is ever intended to sympathize with Sugou, who seems designed to be as repellent as possible right out of the gate. His subsequent and vicious asskicking at Kirito's hands is very well deserved.
- Most of the members of Laughing Coffin probably crossed, being that they're a team of player killers who knew they would die for real when killed in SAO. However, Shouichi Shinkawa/XaXa and Atsushi Kanemoto/Johnny Black definitely manage to cross this by creating the legend of Death Gun just so they could continue to kill. Additionally, Johnny Black crosses this further by attacking Kirito and Asuna on the street whilst on the run from the police, ultimately resulting with Kirito being poisoned, hospitalized, and then dumped into UW by Rath, setting up the events of the Alicization arc.
- Vassago Casals establishes the Laughing Coffin guild with the purpose of having people murder each other for his own amusement, fully aware that any-and-all deaths would have their blames be put on Akihiko Kayaba. A more specific moment is when he beats up and tortures Kirito in front of his True Companions purely to spite them. And then there's his announcement that he will be hellbent on Kirito and Asuna before he brutally murders them in real life. Once Kirito recovers, he reacts accordingly.
- Grimlock crosses this by hiring the Laughing Coffin guild in order to kill his wife Griselda. This would be bad enough by itself, but his reason for doing so- that he didn't like how his wife had become stronger, and wanted to kill her while he was still the person he remembered- proves that he never truly loved her, as Kirito and Asuna point out.
- Raios Antonious and Humbert Zizek were already detestable Hate Sink characters who bullied Kirito and Eugeo, but they crossed the point of irredeemable when they tried attempt to rape Ronye and Tiese.
- Quinella crosses it when she brainwashes Eugeo into an Integrity Knight into fighting Kirito, and later on torturing Cardinal before killing her.
- Gabriel Miller crossed it in his backstory when he murdered his fiancee because he felt her soul would lose her briliance, when he was a child. Seeing the MO of this guy's Satan-based objective in action is truly horrifying. And then he crosses it again upon entering the Underworld.