I'm Australian, so American English can get on my nerves [especially when doing an American crossword; damn your U-free spellings!] but the most annoying one I've found is fairly common online: yea.
And not like "yea, verily", but "yeah" without the "h". I physically have trouble reading anything that contains "yea".
Also "lolol". Are you laughing out loud over lemonade? Lying on luscious oil-coated lima-beans? Licking over long, oval lacerations?