Men are stupid jerks that would do anything for manipulating women, getting them dirty and having sex with them. Women don't need men's lubric perversion. Fortunately, mother nature made man's testicles extremely sensitive, so that women can punish the bad men.
A fillip on a testicle feels like an electric chock and causes intense pain. Women that are aware of that and that are willing to hit hard are a real turn on.

Krebs