several things that are equal in my rage ( hard to pick one):
i dislike something/want something < means > everyone wants it ( or dislikes it). And if you do not want it. you are wrong and bad. ( flying, lfr etc etc)
I hate the game, i hate this and that and that and that < > but still hanging around of forums trying to ruin everyone else their day.
lore stuff like: they think it is this or that < > i proof it with ingame stuff. they say: but this and that. And then i say: yup i know. But blizzard retcons some stuff A LOT. So most recent stuff makes my first statement correct. Per example high elves. How ingame a raid boss/leader of nightborne calls blood, high and night elves all by different names. And yes outside the game ION-cannon has said other stuff. But ingame, in lore its still a thing ( high elves).
But if i HAD to pick 1 thing i really hate:
/qoute wars. where people qoute me and try to find a fault in my text to win. So they will qoute parts of sentences to make their point.
and go in on that point, not reading anything else. Just because they want a win. And not discuss the game.