Using "good" as an adverb grates me at times.
"Vacay," "preggers," etc. absolutely drive me NUTS. Is it really that hard to pronounce vacation and pregnant?
I know I use the phrase "yeah" a lot in email/IM. I need to stop. I also start sentences with "Oh," quite a bit in emails. Need to quit that, too.
Crompsin, when writing essays, tends to use the phrase "in that" more times than necessary. I find myself crossing it out every single time so that it won't appear in his papers at all. He also uses the phrase "hooda buddha" as a general noun. "I've got to go get the hooda buddha ready.." and it drives me crazy because I can't always figure out what noun he is actually referring to.