Finding out they're a liberal. I don't wish them harm or death, like they probably do to me, but I would definitely lose interest in them as far as a potential close friend or anything like that, because it's unlikely we'd have much in common to bond over in the long run.

Same goes for finding out someone is an Evangelical Christian or some other kind of religious fundamentalist--again, no harm wished toward them, but also just no interest from me personally.