I've told this story before a few times in chats on here, but not sure I ever posted it.
I got my first jockstrap when I was around 8 or 9. I played little league baseball, and we were going from coach pitch the previous season to kid pitch. Our coach told us that we'd need a cup because kids would be throwing the ball all over the place. So, my dad and I went to the sporting goods store and bought an adult small cup and supporter. I was a big kid, so the supporter fit me okay, but the cup was way way too big for my body at the time. It made an enormous bulge in my baseball pants, which I was kind of embarrased about, but I got over it the next practice when all my teammates showed up with similarly gigantic cup bulges. Youth sized cups were relatively rare back then (mid-90's) and adult cups only came in one standard size regardless of supporter size. Anyway, we started knocking on our cups like boys do, and pretty soon we went from hating them to loving them. For me especially, I really liked the feeling of my tight supporter hugging my butt and my big cup protecting my boyhood. Made me feel like a big man not a little boy.
Fast forward a few years. I'd developed the habit of coming back from baseball games and practices and stripping down to nothing but either my sliding shorts with my cup and supporter underneath, or just my cup supporter. I'd lay on my bed in my room in just my cup watching TV, or on the couch in the basement. My parents would walk in the room and see me like that and just laugh, shake their heads, and mumble something about boys being boys. One day, I was down in the basement watching tv after baseball, in just my dirty cup and supporter as usual. I'd flipped over onto my belly, and while I was watching tv, I started almost unconsciously grinding my cup into the couch cushion. I noticed that it felt pretty good to do that, so I kept doing it, a little harder and faster. That felt even better. Eventually, it started to feel really good. Suddenly, though, I got a wild sensation in my balls that I'd never felt before, almost like I was about to pee. I felt an overwhelming, pulsing sensation starting in my groin and going throughout my body. I felt some liquid come out of my penis, but it definitely wasn't as much as usually came out when I peed. I went into the bathroom, pulled my cup supporter down and inspected the pouch. I definitely hadn't peed in it, but something definitely happened and I was confused. Then it dawned on me. I'd just had my first orgasm and had ejaculated into my cup!
Ever since then, I've had a big time sexual thing for jockstraps, cups, sports gear, locker rooms, etc. To this day, if I'm worked up enough and rub on my cup just right, I can make myself empty my nuts into my cup while still wearing it, and they're always incredibly intense orgasms.