When you are doing someone in bed, and they let you get through into them because they cannot block your private area from getting into their genetalia, like Huet cannot stop a puck from getting into his goal

A pubic hair piece. A toupee for the pubic area/genitals. In the 1700’s when mercury was used to treat sexually transmitted diseases (Gonorrhea or Syphilis) one of the side effects was the loss of pubic hair. To disguise this condition, that was not cured by mercury, a Merkin was employed.