Green’s Dictionary of Slang

1. the insertion of the hand (and forearm) into the vagina or anus.

1972		B. Rodgers Queens’ Vernacular.
1979		Frank Zappa ‘Broken Hearts are for Assholes’ 🎵 Fist fuck.
1981		J. Hayes in Chesebro Gayspeak 389: The greatest portion of the gay lexicon refers to gay male sexuality and associated activities: fist-fuck.
1985		‘Thommo’ Dict. Aus. Swearing & Sex Sayings n.p.: FIST FUCK (3) — Male homosexual inserting his fist into his partners anus.
1999		Guardian Guide 12–18 June 30: FF (’fist fuck’).
2000		N. Barlay Crumple Zone 31: Ah’m so Christian Samaritans come to me for a fistfuck.
2005		E. White My Lives 122: [classified advert] VGL XXX horny dominant top WS, FF, C&B torture, BB, verbal.

2. an act of masturbation.

[1952		(con. 1948) G. Mandel Flee the Angry Strangers 40: ‘Back to the fist!’ one shouted ‘Go twiddle it like you did last night!’ another screeched].
1985		‘Thommo’ Dict. Aus. Swearing & Sex Sayings n.p.: FIST FUCK — Female masturbation [...] FIST FUCK (2) — Male masterbation, or a poor excuse for a real fuck.
1987		‘Victoria Parker’ Pay for Play Cheerleaders 🌐 ‘Like this then, jerk up and down and stuff!’ she gasped [...] ‘Yes, like that, darling Nancy ... Fuck me with your fists! Gimme a good fist-fuck!’.