I mostly hate the retarded 9,000 meme (and its 1000000+ counterpart, amongst many others). A lot of "nigga"-involving things sound just stale as well, and of course "U mad bro?", "I can smell the butthurt/bitch/w/e", and things like that. Sparta remixes annoy the shit out of me, as well.
Well, those and anything with half a dozen exclamations and question marks typed at once. Then some smilies, including pure-text ones like XD. Keep those in moderation and you're good, otherwise you sound like a repetitive, fad-smitten mess of a member.