Green’s Dictionary of Slang

1. (US/N.Z.) to hit.

1940		R. Chandler Farewell, My Lovely (1949) 190: A plain-clothes man with his coat off and his hog’s leg looking like a fire plug against his ribs took one eye off his evening paper, bonged a spittoon ten feet away from him.
1959		A. Sinclair My Friend Judas (1963) 31: Rarefied taste bongs you on the conk.
1988		McGill Dict. of Kiwi Sl. 17/2: bong to hit, especially on the head.
1990		S. Morgan Homeboy 139: Bermuda was bonging him over the head with her tray.
2003		McGill Reed Dict. of N.Z. Sl. [as cit. 1988].

2. (US campus) to reject someone for membership in a fraternity, club, etc.

1967–8

Baker et al. CUSS.

3. to have sexual intercourse.

1996

Eble Sl. and Sociability 41: Additional examples can be found in many subject areas, particularly in terms for [...] sex (boff, bong, bonk, bop, bump uglies, grub, and pork).