I never thought of getting kicked in the balls as a sexual fetish until sometime early in my college career. Before then, I had always played sports such as baseball, and discovered the pain that every athlete feels when he gets racked (I never wore a cup then as the style left my inner thighs bruised). My sports experiences taught me pain, but it was a self-defense class that taught me pleasure.
My girlfriend (future wife) was a year ahead of me in college and, as a way for her to exercise, she was taking a self-defense course to help her work on her coordination. I showed up to her class one day early as we had some errands to run, and just walked in when she was kicking some guy in the balls. There she was, wearing a pair of karate over-shoes, slamming her foot into this guy’s padded crotch. I was so amazed, and I got so hard, that I had to run to the bathroom to jerk off before her class was over. I'm not sure if she noticed me or not, but we ran our errands and headed home.
Back at the house, she had taken a shower, and I had caught her coming out naked for all the world to see. She has such pretty, firm breasts with the darkest nipples you have ever seen. I was playing with those and kissing her neck when I asked her about what she does in her self-defense class. She went on about how to break out of attack situations, weapons, and vital points. I asked her what some of the vital points were and she proceeded to show me by kissing where they were and by fondling my balls. She said that a guy's balls were his most sensitive area, but that you needed to make sure that you struck them as hard as you could for the most impact.
Before I realized what I was saying, I asked her to show me what it was like to kick a guy in the balls. She giggled, asked me how and asked me if I had a cup. A cup? She said it was so that she wouldn't hurt me so bad, and that we could take it from there. I had a cup from a softball team I was on so I slipped it on and nothing else. I made her wear nothing but a sports bra and her karate over shoes, and there we stood opposite of each other. She lay back on the side of our bed while I stood in front of her. I could feel her starting to rub up the underside of my leg with her foot until she reached the bottom of my cup, and she lightly pressed against it. My dick was starting to hurt from being compressed in the cup, but she said that it excited her to see me in it (I have no idea when that was). After pressing on my dick and balls some more inside the cup, she brought her foot back and started to lightly kick me in the balls.
The thump of her foot hitting the outside of the cup made my dick even harder and the head started to peek out behind the edge. She noticed this and proceeded to squash to bottom part of the cup, which started to smash my balls. I was so hard by this time that I couldn't stand it. I think she saw my discomfort, and reached over and slowly pulled the cup down to my ankles where she proceeded to fondle and bounce my balls while she made me pull my legs apart. She asked if I was ready for some pain, and away we went. Before I could answer, she swung her foot under the bed and kicked me square under the nut sack so that my dick bounced straight up in the air. The cushioning from her shoes took a lot of the blow so my balls felt pretty good. She swung again this time a lot harder, and the top part of her foot smashed my balls with incredible force. I felt the pain of the kick but I also felt the pleasure. I knelt on the floor and she continued to squash my balls with her foot. I felt like I was going to pass out, but then I realized that I was about to cum. The harder she pressed the more I came and she rubbed her foot all over my balls.
From then on, every time she came home from self-defense class she always had a few kicks left over for me. This story is absolutely true!!