No u: often used by a person who doesn't want to have a social interaction, with a mind that can't elaborate a complete sentence informing the other person that he doesn't want to talk, repeating "no u" for every sentence he hear, annoying every person around him.
Universal counterargument to any form of human insult, with the possible exception of ur dad lesbian. It is known to be tougher than Kevlar, and has catastrophic effects on the assailant.