The one that drives me the most nuts is: LOL.
If you are friggin' actually laughing in your home, you don't need to type out some stupid acronym saying so.
Of courses that is followed by unneccesarly 'short-cut' words: kewl (hell is that about?), prolly (idiot), anything that involves the number <8> (h8, l8tr, etc).
On the other hand I have used the words Bah and Owned in real life well before I became a profesional internet junkie.
Woot is another one that kinda bothers me, but I catch myself using it once in a while, so apparantly I don't hate it that much.