Green’s Dictionary of Slang

1. salt beef / corned beef.

1898

Star (Canterbury, NZ) 1 Oct. 7/8: In ‘Darkest England’ [...] corned beef [is called] ‘gee-gee’.

2. (US) the anus or vagina.

1961		R. Gover One Hundred Dollar Misunderstanding 20: He so gee-gee jittery an all, she guess she gonna git his gun wiffout hardly no work.
1972		B. Rodgers Queens’ Vernacular 19: The rectal opening, anus [...] gee-gee[hole] (g?-g?, kwn Wis, late ’50s, fr vul sl gig = the vagina; cf La Creole, gigi, a child’s favorite toy // Gullah gri-gri = a voodoo doll: ‘I’d be willing to bet money that Jim has a tight little gee-gee’).
1974		National Lampoon Nov. 20: They were supposed to graduate last June but they copied each other’s papers for Rem Eng and took a royal doucheroonie up the gee-gee [HDAS].
1989		P. Benchley Lush 56: Don’t knock it till you’ve tried it. Fastest high I ever had in my life. Up the gee-gee, in the bloodstream . . . liftoff!