I don't mind so much the former; it's the latter that bugs me. That or repeatedly saying "X IS A MARY SUE/GARY STU" when they really... aren't, and the person is just trying to justify their hate. If people say "I don't like so-and-so because ______," I'm more likely to take it respectfully than the "I CAN'T STAND SO AND SO BECAUSE THEY ARE A BITCH AND WHINY AND ALSO A MARY SUE AND THEY GET IN THE WAY OF MY PAIRING" and etc.