Humping off

Lem had a standing offer — if a man jacked him off one time “wit’ full throat” — swallowed his cum, basically — Lem would let him “hump off” on him bunches — Lem spent years prison, so he knew about all this stuff. “Humping off” was when you rubbed your dick on his back, in the crook of his elbow or between his thighs.

From Roughnecks Got Oral Needs!