I agree with Throbert on the "too cool for school" analogies. I think the statement is generaly saying, "I'm too cool for school, (and therefore) too cool to act like this." Although I would say, Lena, that its probably more of a young urban phrase, because quite frankly I've never heard it said around my part of the world...lol. If you're into the gang slang and hip hop, urban type language, it may be used more often. Definitely from a youthful vocabulary, though.