Green’s Dictionary of Slang

(orig. US) to talk nonsense, to prevaricate.

1900		Howitzer (US Milit. Academy) 1 138: Be-esse – To talk crudely [HDAS].
1962		(con. WWII) J.O. Killens And Then We Heard The Thunder (1964) 15: Think they can B.S. around for the whole damn duration. [Ibid.] 194: Solly and Worm were seated in the orderly room Bee-Essing.
1972		O. Hawkins Ghetto Sketches 131: Get to the point, brother! And stop b.s.in’ ’round!
1982		(con. 1970) J.M. Del Vecchio 13th Valley (1983) 84: Moneski [...] smoked a lot of cigarettes while the others were BSing.
1995		A. Heckerling Clueless [film script] Spare me the lectures on how driving is such a big responsibility, and you can’t B.S. your way through it, OK?
2001		A. Schulman 23rd Precinct 65: ‘Someone said that there were eighty people killed [at a major fire]. I said, ‘Stop BS-ing me’.