What is N't?
1.
universal negative. One can say this at the end of a statement to completely reverse the whole thing. Commonly used to disprove a friend and make him/her seem foolish.
Guy #1: Who lost their keys the other night?
Guy #2: Kevin did!
Kevin: n't.
Guy #2: *blushes*
2.
the ending of didn't
n't tell you to sit down