Green’s Dictionary of Slang

(Aus./US) the penis.

1966		Trimble 5000 Adult Sex Words and Phrases.
1972		B. Rodgers Queens’ Vernacular.
1993		B. Moore Lex. of Cadet Lang. 275: pogo stick 1. rhyming slang for prick (penis) because ‘it was made to bounce up and down’.
2003		B. Dark Dirty Cockney Rhy. Sl. 88: I wouldn’t mind her bouncing around on my pogo.