Green’s Dictionary of Slang

(US gay) mutual cunnilingus or fellatio.

1954		(con. 1940s) T.A.G. Hungerford Sowers of the Wind 145: Likes his vice versa [...] I always thought he was a bit of a horse’s hoof!
1965		Guild Dict. Homosexual Terms 48: vice versa (n.): Mutual cunnilinctus.
1972		B. Rodgers Queens’ Vernacular 182: to participate in mutual orogenitalism [...] vice versa.