People who are horrible to others for amusment piss me off big time. This is because I had to put up with being at the recieving end of this crap for 5 years at school (which I have only just left), and it's just not right. I mean, what did I (and anyone else who puts up with/used to put up with this kind of thing) do?
People who slag off others behind their backs also pisses me off. If you say these things, whats the point of saying it behind their back, they aren't going to know, are they, so it's not exactly going to wind them up unless they know you're saying that crap behind their back.
I'm also pissed off by overrated crap. I'll give some examples of the overrated crap that I hate: Twilight, Almost everything relating to Disney (very few exceptions) (especially High School Musical), Football (or soccer as it's called in the US), Talent Shows on TV (e.g. Britains Got Talent), and most music in the charts. The reason overrated crap pisses me off is because almost everyone just goes on about it, and I have no freaking interest in it!