What drives people to make death threats in private messages after the game?

ComfyTank, on Jan 26 2021 - 14:22, said: I randomly got a very nasty death threat from someone after the game.  I didn't play arty, nor did I play particularly badly.  All I did was shoot their tank once with my O-I for 400-ish damage.   I looked up their profile on the forums, and they looked like a reasonable person.  They were applying to be a Sheriff, and offering to help people learn the game.  They are in one of the best clans, and I often see people from that clan posting on the forums.  I would never expect someone like this to behave this way.   Sometimes It's surprising what depths reasonable-looking people will sink to, out of nowhere.  Have you ever seen someone you thought was reasonable act this way?  A friend, maybe?  Have you yourself behaved this way?  What causes people to act this badly?