Lust in America (1985)

After a cocktail party, three couples stay on to talk about their fantasies. The women trail off into another room, however, and relate all the juicy details on their numerous affairs. Left alone, the men fall into the same kind of sexual "shop talk" as well. What their respective mates don't know is that they have shared some of the same partners and didn't know it! One particularly sex-hungry female hairdresser seems to have made the rounds with all the couples and her presence is felt in more ways than one.