Green’s Dictionary of Slang

to sodomize.

1970		A. Sillitoe Start in Life (1979) 347: If he pansies after a young man he’s buggering his son [...] If he gets off with an older man he’s being bummed by his father.
1999		(con. 1979–80) A. Wheatle Brixton Rock (2004) 33: We used to say some housefather was bumming him.
2000		M. Manning Get Your Cock Out 57: When I was seven the fucking idiot started using my arse like a dartboard, bumming me stupid every fucking night.
2004		P. Howard PS, I Scored the Bridesmaids 158: I said, ‘Hello,’ not, ‘I wanna bum you.’.
2011		Internat. Independent 19 July 37/3: I fantasised about Piers being bummed in prison.
2016		Times Online 15 Apr. 🌐 CW was told so much amazing gossip that [...] it actually compiled a Rolodex of gossip in which ‘B’ — for ‘bumming’ — was 38 entries long.