Most of us ought to know the phenomenon (as Marc mentioned in the comments in a previous post) where the fact that something has become popular now means it sucks. We all know this one; we just don't know what to do about it.
Fandom is insular by design. The fact that "we" like something means there are hordes of other people who do not like it, or at the very least do not know about it. And since we, the fans, do know about it, it is our mission to bring that liking to others and make sure they like it, too. Thus, browncoats.
What ticks off fans even more than other folks knowing about their beloved X and hating it anyway is when those other folks find out about X without their help, thank you very much. Doubly so when it happens on such a scale that they feel a massive opportunity has been missed — not just to be the ones to bring word of X to the masses, but to be able to claim responsibility for doing so, and to thus validate all the more the investment of their time and energy in fandom.
I just looked back over what I wrote in those last couple of grafs, and the convolutions involved are severe, even for me. Is there really that much of an evangelistic bent to what fans do, that much of an urge towards validation? For some, yes — especially for those who have a good deal of emotional weight vested in that validation. This goes for Mets vs. Yanks as well as Team Edward vs. Team Jacob; it doesn't matter what the underlying material is.
I'd be dishonest as hell if I didn't own up to a little of this myself. In the earlier days, when I wrote about this or that obscure Japanese movie, I would have had more than a few layers of skin peel off if someone sniffed in my direction about it. (Some did.) I was under the belief — not entirely delusional, but functionally so — that if I simply explained my reasons for liking something well enough, then that explanation would transform itself into a transmitter of taste, and the other guy would end up liking it too because I'd convinced him it was worth liking.
The problem is, taste doesn't work like that and never has. Taste is something you form first and then contrive a defense for. Nobody gets talked into liking something; they like it first (even if only covertly, "from behind the stove and beneath the floorboards") and then talk themselves into it, or retroactively agree with the arguments presented to them about why it's great. I told myself I hated the Swans the first time I heard them — although what I was really saying to myself was, "If I tell anyone else I like this I'm going to be considered hopelessly uncool, so I'd better rehearse my reasons for hating it." Defending what was sure to be an unpopular preference wasn't something I had a great deal of experience with. When I later learned some of the finer points of doing it, I found an even more essential revelation was waiting after that one: few tastes need to be defended anyway.
I'll have more to say on this after the first round of tomatoes are flung.