A vagina. A poontang. A beef curtain. A cunt. A twat.
You put the peen peen in the poon poon.
An exclimation made by a man who is certain that he is about to recieve some kind of intercourse, be it a cheeky blowy or full on balls deep poon pounding.
The words are usually said with assonance of 'choo choo' (like a train') and the arm movement commonly seen when a train driver is honking a horn
Danny: that nasty bitch Jenny is gonna feel my balls slap on her gooch. Poon poon!