How often should a guy get kicked in the nuts?

As often as he harasses or attacks others.

Considering that it's one of the soft spots on a guy that women's self-defense classes teach us to hit (only as a last resort) I'm going to go with @YoungPoet345 comment that he should get kicked there as often as he assaults others.

Im votin never

Coming from a guy this is an odd question.

as many as required to bust a nut

There is a suggested number???

Uhm... never, I hope 😦