"Not!" as an
exclamation negating the entire
sentence before it was
popularized by the two
Wayne's World movies. So much in fact, that people here in
Norway still walk around saying "NOT!".
Example : "That's a nice shirt! NOT!"
Before Wayne's World, the American band Anthrax used the expression quite a lot. They had a mascot called "The Not Man", their guitarist Scott Ian shaved "NOT" onto his chest (he is a hairy man), their merchandise t-shirts and caps had "NOT" printed on them etc. The exclamation of "NOT" was also prominent in their hit single "I am the man" (which interestingly enough precedes both Beastie Boys and Rage Against The Machine in mixing metal and rap). I once read an interview with Anthrax, where the origin of the phenomenon was discussed, and they managed to date it all the way back to 1976, remembering it being said by some kid from Brooklyn, Queens or Bronx (can't remember).
Phew, that was an interesting node. NOT!