Poor (by poor I mean terrible) spelling and grammar gets to me in ways I can't describe. I think it's because I have no respect for lazy people. I'm from Norway and I'm perfectly fluent in English, both pronunciation and grammar. Naturally, an English person should be better at it than me, but in most cases they are not - which means they are so lazy they didn't bother learning their own language.
Also, I'm irked by arrogant French and German people who stubbornly refuse to learn English because their languages are 'just as good' - I have news for you, they're NOT!
And on the top of the heap of annoyances lie the typical American. The word 'Soccer' infuriates me to hell, and I'm prone to smacking people right over the face (or worse) if they ever used the wretched word in my immediate vicinity. It's called football. Period. And on we go with the 'u' cleansing of American English. Colour =/= color, flavour =/= flavor etcetera. And heavens! The removal of endings reveal a person as one I'm unlikely to deign to conversing with. Examples of that is chillin', readin', drinkin' - aaand by now I have a splitting headache.
Chinese people trying to speak English are usually just cute or funny. That is some of the best entertainment around.
Other than that, none of the others annoy me, except I wouldn't bother reading any 1337 speak.