People who text talk, It drives me insane! Even worse people who put "X" or multiples of at the end of every message, irritates me more than I admit.
Adults who can't use their, there and they're properly or "our" and "are". It irrationally annoys me, just spelling in general, if you can't spell, don't talk to me.
People who are vulgar, I once had a drunk guy come up to me and straight away ask to perform oral sex on me. Bless him I doubt he'll ever approach another woman in public now but it still shocks me 4 years on. I found his behaviour disgusting.