Niff is a street name for poppers.
also used for sniffs,

To sniff and lick at the same time. usually done by a man to a womans vagina.

an abbreviation for niffler. its derived from the creature in harry potter which sniffs out gold, but it simply means "nothing" or "nevermind." see niffler

An English 50 pence piece. Hand in hand with biff

a great person hu is fun 2 b around n always cumz up wi random topics ov conversation. it is normally a blonde and short female hu is great 2 have around!

A word to say when you don't know what else to say, especially when bored.

Jack-off into the hand of someone, and get it all nice and sticky. Tickle the person's face with a feather or such and see what they do...