Green’s Dictionary of Slang

to copulate with.

a.1650		ballad in Wardroper (1969) 195: And I can sing nig-nog, / And well I would nig-nog thee, / And sell my petticoat, smock and all / And pawn my C—t for thee.
1925		E. Field ‘A French Crisis’ in Facetiae Americana 19: She’d nig-nog, duffle, snuggle, concomitate and quag.