I know a few Jhin mains that got chat restricted/banned for toxicity, but they are generally nice and pretty chill.
If I had to say most toxic, my money would be on Yasuo mains. Its always a gamble with these assholes. Will they actually play the game and hard carry, or will they say "fuck it" and int because they feel like it? Will they acknowledge the fact that they made a mistake, or will they blame the team and troll them for the rest of the game/afk?
Maybe I'm a bit biased here because I just got out of an ARAM where our Yasuo main got 2 kills, disconnected, came back, sat in fountain, only bought
, and ran out to feed the enemy a kill so he'd still be considered "in the game", but whatever.