Is this guy a psychopath? He was a "quiet one"?

[Yeti]

Especially this single instance doesn't show that he's a "psychopath." And being quiet doesn't really mean anything for that anyway. It sounds like this was more a response by Trevor to Justin's excessive bullying. Sometimes people simply try to handle such things in a civilized manner, and when it doesn't work, they can sort of snap and their "self-defense" can go excessive and over the top. Sooooo, a bit of an excessive response, and the kind of thing that happens when bullying persists and nothing civilized gets done about it. But no, Trevor the quiet kid isn't a psychopath based on this. The psychopath is far more often the persistent bully, who lacks empathy for others, and just gets their kicks making others suffer. And unfortunately sometimes the only way to get such behavior to stop is to match or exceed it. We just normally like to have objective legal systems for matching or exceeding things (and do it via handcuffs, jail, etc.).