Green’s Dictionary of Slang

used to describe a promiscuous woman, e.g. find a woman with margarine legs.

1987

K. Lette Girls’ Night Out (1995) 187: Surfers are an amphibious, beach-dwelling species, who hunt in packs for females with ‘margarine legs’ You know, easily spread. Chicks are nicknamed bush pigs, swamp hogs, maggots, spitters or swallowers.