The most toxic communities I know of are the Genshin community, Payday 2, FFXIV and source games communities in general.
Eve Online where, as long as you’re not telling your victim to use real world money to buy things before you scam them, anything goes.
The thing about EVE is that caveat emptor is the social contract, and as long as you don’t get your dander up about being pirates or scammed, the “bad guys” are more than willing to help you learn to avoid the next trap. I was once part of an “anti-piracy” roaming fleet that got bored with the quiet night, and ended up jumping a newbie who was hanging out where they shouldn’t have been, tackling his ship, and proceeding to ransom it back to him for the princely sum of 1 ISK while we laughed our heads off in Teamspeak. Then we sent him on his way with a few hundred thousand ISK extra, some pointers on highsec versus lowsec, and the valuable lesson that there were always sharks on the prowl for easy prey.
Escape from Tarkov
It’s pretty broad but I have met some truly awful human beings playing Minecraft. the “community” as a whole is… fine? for a game community, but the individual pockets you find can be truly horrifying. Hell, even in so-called “friendly” communities you can meet some pretty terrible people. People treat their servers like little fiefdoms, and all the toxicity with a fiefdom comes with that.
just throwin in another anecdote that XIV has had one of the best game communities I’ve experienced, even when the game gets pretty stressful in endgame content.
Most MOBAs are pretty notoriously bad, though Heroes of Newerth was definitely the worst one of those i had played.
Anecdotally, my personal worst experience was with FFXIV, which was probably exacerbated by how much praise that community gets otherwise. The Novice Network system they have is a mess, new players are put into a channel with a bunch of “mentors” that don’t really want to help anyone, at least on the server I was on. They either wanted a global chat channel for their own use, or just wanted the cosmetic rewards mentors had on offer. I remember one actively trying to get new players to quit if he found out they had come from WoW. The channel is entirely self-moderated, and mentors would kick people out just for fun. It’s an AWFUL first impression for newer players.
One thing WoW definitely does better with their Guide channel is giving literally no tangible rewards to guides, if somebody is opting into being a Guide it is only because they want to help new players, they get nothing else for it.