Not sure "uncool" is the right word, but a couple-few brands I have an irrational (or maybe not) aversion to:
1) Trek - don't like the way they put all their credibility in the basket of a guy who was pretty well known to be a doper, and trashed the clean guy who said, when asked, yeah, he might be a doper. Also had bad experiences with two LBS that are Trek-heavy.
2) Diamondback - this one really doesn't make sense. My dad has a Diamondback MTB that's almost 40 years old and still going strong after a lot of hard miles. Then they became a box-store brand. Now they've got a mega-$ tri bike. I have to admit this is snobbish of me, but if in the extremely unlikely event I was going to spend new car money on a tri bike, I'd kind of like to have some brand cachet. Roadmaster could come out with the greatest tri bike in the history of the universe tomorrow, and I'd still have a disconnect about paying elite money for something with the Roadmaster brand on it. Hey, I said this was irrational, and doubly so because I'd never spend that kind of money on a tri bike in any case.
3) Specialized - don't like the way they tried to crush Volagi and Robert Choi, when Robert was just trying to make a product that Specialized had said, definitively, they had zero interest in ever producing under any circumstances. OK, sure, IP law and whatever. But if you're saying you're dead set never to build this bike, why can't you let the guy go off on his own and build it himself?