This bloke that used to slag off any band I played in, except when I joined one that he already loved and he ended up liking one he never knew I was in. Used to advertise some of our stuff so people thought he was a top bloke, get people into his label's online store and stuff, but was never interested in stocking anything of ours. Glad to see his label has gone bust recently.
Also can't stand prick gig organisers that promise a bar tab and a cut of the door takings, then at the end deny both because they reckon they had to spend it on security and sound techs.
Then there are general groups of people:
Pseudo-intellectuals: also can't stand know it alls.
Goths: one of the worst trends ever. Used to play in a lot of metal bands so always had to associate at certain stages with these miserable pieces of trash. For the record, none are hard done by, and none are from poor backgrounds. 90% are also pseudo-intellectuals.
Hipsters: mostly pseudo-intellectuals. Also douche bags because they think if you're not familiar with the obscure tripe they crap on about then you're not even fit to carry their bags. All of them also deny being hipsters and reckon they dislike them too. This is because they actually do in fact think their deep and intelligent.
Extroverts: get a hobby you knob heads. Stop moaning on Facebook that you aren't going out on the weekend.
Chronic complainers: bugger off. I'm not interested in your negativity. Get a hobby and stop complaining. It's not healthy to be negative all the time.
Current generation of video gamers: always trying to talk to me about 'old school games' and how they grew up with better games. Bugger off you did. I was raging at games like Catacomb, Battletoads, and even Sonic before you were swimming laps in your dads nuts. This also applies to anyone who says they've been playing Call of Duty since the start but they're actually only referring to the first Modern Warfare. News flash, there were 2 PC CoDs and one expansion, and one console CoD prior to that. Trend whores. This too applies to anyone who only owns a Wii and says they're a gamer.