Green’s Dictionary of Slang

performing an act of cunnilingus.

1949		Monteleone Criminal Sl. (rev. edn).
1965		Guild Dict. Homosexual Terms 31: muff diving. Cunnilinctus.
1977		D. Powis Signs of Crime 193: Muff diving Another taboo and gross expression meaning the practice of cunnilingus. Never used in mixed or family company.
1980		Maledicta IV:2 (Winter) 188: It may mean that he can only eat her (i.e. go muff-diving, or muff-noshing). [Ibid.] 198: On the other hand they may indulge in a 69, with reciprocal muff-noshing and knob-gobbling, if they are both linguists.
1984		(con. WW2) T. Jones Heart of Oak [ebook] There I was to learn all about ‘Hawsepipe Harry ’ and the golden rivet, and muff-diving and how the snotties were mostly all prats, and how to strangle a baron.
1987		in Delacoste & Alexander Sex Work (1988) 50: I liked it and it really turned me on [...] I did it for a guy in trade for hours of expert muff diving.
1993		B. Moore Lex. of Cadet Lang. 240: muffdiving the act of performing cunnilingus.
2006		T. Dorsey Big Bamboo 136: No cornholing, no tittie-fucks, pearl necklaces, muff diving or golden showers.
2013		T. Robinson Hard Bounce [ebook] His buddy wore a backwards old school Patriots hat and a Muffdiving Instructor T-shirt.