Not is a wonderful word. Much like allegedly, it can be used at the end of a sentence to automatically discredit everything said before it. An example of this, taken from a real life conversation:
- Man 1: "So yeah, you won the lottery last night..."
- Man 2: "Really?"
- Man 1: "...yeah..."
- Man 2: "Wahey! I'm off to the pub!"
- (Man 2 leaves)
- Man 1: (some time later) "...not"
- (Man 1 sniggers to himself, looks around for Man 2. He ain't there: he's in Barbados.)
Warning: do not use this around irritable people or the easily led.