Hmm, interesting! I'm a man myself, and to the best of my knowledge don't sleep with my hands near my groin. So it feels like maybe whatever it is, either the discomfort of the situation, or the cause of the situation, might lead to it in some way?

For me - it’s cats. They know exactly where to jump on the bed while I’m asleep. I try to side sleep now but if I’m on my back I’m protecting 😂

Your post leaves me with a lot of questions. But as for the hand in pants thing, they probably had siblings or roommates at some point who thought it was funny to wake people up by tagging them in the balls.