I really hate it when people misspell "lose" as "loose". That just seems to bug me more than any other common spelling mistake, for some reason.
I've also come to really hate the people who believe that unless you started out with Gen 1 or 2, you're not a "true" Pokemon fan. Oh, I'M sorry I was born 3 years too late! How silly of me!!! o_e On that note, "hardcore" gamers in general. If you don't play Call Of Duty/Halo/Battlefield/Whatever, you'll never live it down.
Broken/slow machinery also drives me nuts, As well as people who act like they're so great and amazing when they're really not. What's worse is that I'm afraid I might be that kind of person without even realizing it >.< I'll say something, and then realize later that what I said was incredibly stupid, and there's no way to take it back because that person is gone. ;-;
The thing I hate most, though, is being told what to do/how to do something. I'll start panicking and then I'll feel all guilty, because if I listen to them and let them practically do everything for me it means I'm a useless who can't do anything, and if I ignore them I'll most likely mess it up. And then people will give me all this false praise and I'll walk away feeling terrible, and then they call me an ungrateful for it. I don't mean to be ungrateful, really, but I just want to earn the compliments I'm getting >.<