I hate:
"Awesome" - The Grand Canyon, Victoria Falls, and the miracle of childbirth are all 'awesome'. Your ice-cream isn't.
People that finish a sentence, wait, and then say "not!". You people need to go fxck yourselves. I really mean it.
People that deliberately mis-spell words to try to create a new 'cooler' word. eg. 'Kewl', 'Phat', etc. WTF?
Oh, yeah, and "Phat" deserves its own mention. What a totally wxnk word.
However, my least favorite of all, is any time a company has an 's' at the end of its name, and change it to a 'z'. EG. 'Hopperz'. Do you really feel that just made you cooler?