This is a real story, it happened to me yesterday (actually today, since it was at 6am or something like that).
I am 20 years old, and I had never been busted before. Many girls tried to hit me there, but they missed, so it practically didn't hurt at all. At first I didn't know if that was what was happening, or if girls hitting me there when I was aware of it didn't hurt me (especially after reading that this was what happened to Knackers).
Anyway, after coming home at 1am from going to an amazing rock concert with a friend, I went to a chat room (actually a lot) and started talking to people. I found this girl who is 23 (who trained karate for 5 years and had quit like 3 years ago), and after my usual fighting talk, I kept saying that she wouldn't be capable of actually hitting someone in the nuts on purpose and she kept saying she would. To make a long story short, I was seeing her in person a little while later (at like 3am).
She's an amazing person, and so is her girl roommate. She's a little shorter than me (I'm 1.77 m high) and quite pretty. But when I was alone with her at the entrance of her building, I told her to hit me there. She actually couldn't believe that I was actually willing to let her hit me but after a lot of, "I can't believe this, I'm really going to hit you", she finally did it. This was when I first saw her before going up to her apartment and meeting her roommate. I told her to knee me softly so she'd see it wouldn't hurt me and then start kneeing harder. And so she did. She kneed me a couple times, and except for the last knee, it nearly didn't hurt at all, just like before. Her last knee hurt me enough to make me a little "uncomfortable" a little after she kneed me but I didn't have any problems standing up and I could have hurt her if I wanted to.
After staying with both of them talking for quite a while, I said I was leaving and she came back with me to open the door. That's when I asked her to try and kick me. At first the kicks were awkward, kind of like raising and then like pushing forward with her foot. I think she got my dick once but none on my balls so it didn't hurt much. I then told her to try to kick me in a way I've seen on a femaledom video I got somewhere (the filename is "femaledom4.mpg"), sort of like a mae geri raising the knee a lot, like she was kicking to the face but being closer so the kick would hit my balls. And I'm happy this kick actually worked :) It did kick my balls and it did hurt. I didn't fall down, double over or anything, but it actually hurt. She was barefoot and she wasn't kicking nearly as hard as she could but I had been kneed before so I was a little more vulnerable. She didn't look like she wanted to go on with it, so I told her that if she kicked me full force once, it would be enough. She wasn't angry at me or anything so she couldn't really kick me as hard as she could but she kicked me many times more (she even missed on some of the kicks). During her last kicks, I couldn't help but moving a little so they didn't hit as they should have. I told her to really kick me hard the next time and I closed my eyes so I wouldn't try to dodge the kick. And it was her hardest kick that day and the one it hurt me most. I felt like I really needed to lay on the floor but I only ducked for a few seconds (the more I showed her it didn't hurt, the harder she'd kick next time). I still would have been able to fight her and beat her if I wanted to. I left her home at 7am.
The bottom line is I enjoyed like hell being busted for the first time. But I found out what I wanted to know, which is if a girl could really beat me up if she hit me there. And my answer is NO, if I think she might kick me there. But I know kicks work better (at least for me), since her knee couldn't really get in between my legs even when I was spreading them apart a little (not a lot when thinking of being kneed but much more than how I normally stand still). Her little girly foot went straight to my balls with no obstacles. But still, after being kicked once and again by a girl who used to train karate (even if she lost her training) didn't disable me at all. It did make me lose my appetite though :) I still have to try what would happen if she'd squeeze my balls (though I think this girl won't do it) and what would happen if she kicked me when I'm not expecting it.
Anyway, that's the story.