I think hatred on reddit is a complicated mess of legitimately bizarre people being given a forum for the first time, trolls, signalling, and groupthink, depending heavily on the topic and subreddit.
Signalling of social and political grouping is particularly prevalent and obvious on the internet because you can't rely on extrinsic or physical factors to demonstrate your social groupings. In the real world someone can rely on their appearance to telegraph a lot of things--clothing and grooming choices alone can hint at sexuality, politics, social class, and a variety of other things, to say nothing of existing social structures and bonds (who you surround yourself with also telegraphs a lot). On the internet, you either need to explicitly say these things ("I'm not straight", or "I came from a well off family" or "I'm a conservative") or signal them somehow, and there are areas where it's less acceptable to overtly announce your membership in a group, so implying it through general biwords for it is socially necessary. ("I'm filthy rich" or "I'm really, really smart and intellectual" or even "I'm really, really, really ridiculously good looking" all likely fall under that category. I think that generally the more desirable the category, the more it requires either actually costly signals--e.x. displaying expensive artwork in your home or donating lots of money in the case of wealth--to do 'acceptably'.)
You see some of it on HN, too, although I think it's generally much less accepted to negatively signal here--but especially in the more social-justice-y threads, you see a lot of signalling of people picking sides going in both directions, because that's something that HN doesn't really have any sort of unity on but individuals here feel strongly about. In this thread there was a perhaps unsurprising backlash against the author (usually backed up with some logic--which is thankfully required by the etiquette here) about why the posters were justified in their active dislike of sports.
In my experience most social signaling/biwording is fairly well summed up by the basic theory of "You will only expend effort signaling if there's (a) a chance you'll be mistaken for someone in a group you don't want to be mistaken as, and (b) there's a chance you'll be seen as being in the group you want to be in because of it."
