Green’s Dictionary of Slang

(US, mainly milit./campus) to impose on, betray or otherwise inconvenience a friend; thus buddy-fucker n., buddy-fucking n.

1966		in IUFA Folk Speech n.p.: Denotes asking a friend for money. Buddyfuck [HDAS].
1967–8		Baker et al. CUSS 89: Buddyfucker, play. Take someone else’s date away. Buddy-fuck. Take someone else’s date away.
1973		Eble Campus Sl. Nov. 1: B.F. – acronym for ‘buddy fuck’, to do wrong to a friend: I’ve been B.F.’ed.
1985		D. Tate Bravo Burning 161: Wash your mouth out ... buddyfucker.
2000		Sex-Lexis 🌐 International fuck-your-buddy week Or: buddy-fuck week / fuck-your-buddy week, a special week in the year when the betrayal of one’s friends is allowed. Rare; military and college usage.