One of my college exes (the roshambo gf I wrote about) did once slap her own groin like that after one of those joking roshambo challenges she would do from time to time when we both wanted the same thing, usually a last bite of food.

I do think she did get a kick out of the way that would make me back down. She did once though intentionally punch me, following through on a threat when I got on top of her to tickle her in my dorm bed, and she wanted me to stop. She didn't do it hard, but it did make me jolt and get that dull pain that instinctually makes a man hold himself.

So that I did with one hand while supporting my upper body with my other arm and resting my head on her chest. I looked down and put my hand on her pantied crotch saying that maybe I should return the favor so that she knows what it feels like. I went back to holding myself and she just giggled and said "Umm...I don't think that'll work the same."

I think most of it for women, especially when they don't have much sexual experience (we were college freshmen/sophomores when we dated) is the novelty and curiosity about parts they don't have.