Green’s Dictionary of Slang

1. (W.I.) the buttocks, the posterior.

1942		L. Bennett ‘Sweepstake’ in Jamaica Dialect Verses 30: But wen me ha’ mo’ time me sey / ‘Ski bam bam chinka po’.
1953		G. Lamming In the Castle of my Skin 44: I nearly did dirty myself when I saw him bring that belt down on yuh bam-bam.
2000		R. Antoni Grandmother’s Erotic Folktales 9: The only coca that grew there now was cocoplumbs in the shape of bambams!

2. (US black) sexual intercourse.

1981

W.D. Myers Hoops 127: ‘How come you never hit on me?’ ‘That ain’t what we’re about,’ I said. ‘You know, we ain’t about no bam-bam thing’.