there is a pretty serious hardcore subculture of this...i can show you huge threads of this stuff on fetish forums...
i honestly do not get it, but if people choose to indulge i wouldn't tell them they could not or should not do it.
having gotten hit in the nuts before while playing sports or horsing around or whatever as every guy has gotten hit a couple of times, i cannot understand why someone would willingly allow them to kick them in the balls...
the pain from just a minor hit in the balls can be extremely unpleasant...getting a direct, hard kick to them seems utterly horrific...
i have to say, from a medical standpoint, this has to be extremely dangerous on a variety of levels for the damage it can do...a ruptured testicle would require removal...i cannot understand how having someone kick you in the testicles with brute force, could be considered fun, arousing or anything else...but some people like pain...
it is the same level of total horror that i find CBT...i cannot imagine how people can enjoy someone utterly mangling someones privates...needle play, and some of the things they do are utterly horrifying...i just do not get it at all.
i can understand some people liking a hard spanking, maybe some whipping, breath play, and lots of stuff like that...but having your genitals mutilated with sharp objects is borderline insanity.
but we live in a rather strange world.