Used in chat rooms or on comment boards. Stand for "incredibly stupid: not!" It basically means that a certain idea, subject, gossip or news item is cool or clever.
<Johnny777> says: hey i heard marys gonna skip school on the day of the test
<Raj8734> says: is:not! i think i'm gonna skip 2

or

Terry89: hey every1, who thinks Jamie dying her hair pink is:not?
by Sandra8888 April 27, 2008
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