A few years ago I had a guy once attempt to negate my opinion on a relatively recent film because I liked "a lot of old black and white movies", in another instance, a guy I knew who had never seen The Warriors before I showed it to him, virulently dismissed it in front of other people based on his impression of it being "stupid" and "bad"; no other critique outside of that. I got pretty heated over the latter incident. So I guess it bothers me when people hate something that I love, but do so out of a place of complete ignorance.
If someone hates something I love, but they actually know something about whatever medium the subject of conversation happens to be in, even if I think they're full of shit, I can deal with that, but I cannot deal with people that are just plum stupid about it.