As you can tell by my username and pic, I am one of those "Bronies"
However, I am not the demanding or hateful sort. Those types drive me crazy, and I HATE when people sexualize or infantilize material of that show or any other!!
Ugh!! Unfortunately, that fandom has become pretty toxic over the years, I have to admit, but it doesn't stop me from liking MLP FIM as much as I do. As for other fandoms I find toxic?! Hmm...let's see...EVERY!! SINGLE!! ONE!! Lol!
I seriously can't think of any fandom that isn't obnoxious...although someone here mentioned Homestar Runner, and I think they're right. I haven't encountered fans of HR who have been rude or annoying to me.