ICP - short for Insane Clown Posse.
When something is rather great, more amazing then great it then becomes ICP.
When a person preforms a great act, nay an amazing act of any kind they are ICP.
Used by the Armadale mang
Dylan: Did you hear about the other night mang
Mang: No what happened?
Dylan: We got heaps of free #2's and I burnt down MacDonalds.
Mang: Sounds ICP.
Dylan: Definately ICP, no doubt about it mang