Green’s Dictionary of Slang

(US gay) a passive male homosexual, poss. a male prostitute.

1989–2003		R.O. Scott Gay Sl. Dict. 🌐 b-boy: Bottom boy, someone who likes being screwed. Also butt-boy, somebody who has a muscular bubble butt and likes getting fucked. It have [sic] a connotation of prostitution.
2021		J. Ellroy Widespread Panic 191: Ruff trade tricksters and buff B-boys.