every fandom. all of them are being represented by little stuffs who think the show/game/book/whatever is the best thing ever and will not accept anyone else's opinions. doesn't matter what it is, if it's extremely popular on tumblr, i expect the fandom to be stuff.
every "fandom" constantly needs to shove their stuff down everybody's throat instead of just enjoying whatever it is that they enjoy alone, or with other people who like it.
if i had to select the cringiest fandoms it would be FNAF, mlp and steven universe
EDIT: actually nvm that last one, it's not very cringy but it's just that the idiots in the fandom (who are in the minority) are the loud ones that seem to be representing the entire group