Green’s Dictionary of Slang

1. (US) an extremely unpleasant person.

1979

Easyriders Dec. 6: A pretty crafty way [...] to get us bumfucks to read your rag cover to cover [HDAS].

2. (US gay) a sexually inadequate partner.

1972

B. Rodgers Queens’ Vernacular 107: Sex partner whose performance was inadequate. [...] bum fuck.

3. anal intercourse.

1879		[G.A. Sala] Harlequin Prince Cherrytop 4: Cunt fuck, front tuck, he shall never once begin it, Crumb fuck, bum fuck, not another peaceful minute [Simes:DLSS].
1899		Horn Book 42: When we hear talk of buggers, the vision immediately arises of men violating the puckered, brown apertures of their fellows. But the[re] are many pederastic amateurs who hold the culminating bum-fuck in horror [Simes:DLSS].
1904		‘Jacobus X’ [trans.] Crossways of Sex 70: ‘Get along, you old cow; aren’t you ashamed [...] Why you’re pleased to get hold of ten sous by a b— f— on the fortifications’ [Simes:DLSS].
1972		G. Legman More Limericks 205: He swore he would screw ’er, / And make her his whoo-er, / But at all but a bum-fuck did fail ’er [Simes:DLSS].
1974		Graffito (Newcastle, NSW) I want a bum-fuck [Simes:DLSS].
1989		J. Morton Lowspeak.
1993		T. Jones Pugilist at Rest 119: Neither of us likes to think of these details and instead we make love – bum fucks for both of us.
2001		J. Hayes Great Austral. Bk Limericks 140: For he won Lotto twice And, against all advice, Let his friend, who was nice, have a bumf**k! [Simes:DLSS].