From reading many of the stories here, I think mine is unique. I hope it doesn't offend anyone's sensibilities, but I felt I had to relate my story.
My father was in the marine corp. He was very strict with me when I was growing up. In my bedroom he installed a kind of hand rail on the wall. It was like something you could grab hold of in the shower or in a handicap stall in the public bathroom. When he first installed it, I had to reach above my head to grab hold. Now it's about eye level.
The purpose of the rail was for when I did something bad or got poor grades at school, he would make me grab the rail with both hands while he paddled me on my ass with this big paddle. Sometimes he would use his belt on my back, ass and legs.
I had to keep holding the bar. If I let go, he would wait until I was able to hold it again and resume the beating until I had received the prescribed number of wham-o's. That's what he called them. He would not leave my room or let me leave until my punishment was complete. So it was best for me to hold on and get it over with as quickly as possible. Oh, and by the way, I had to strip naked.
I was 17 the last time I was punished in this way.
Now I'm here to tell you that I believe this profoundly shaped my sexuality. I need pain to have an orgasm. And that makes it hard to masturbate alone, well it's easy to masturbate, but it's hard to have an orgasm unless I'm in some sort of pain. So when I find the rare boyfriend who's willing to beat me before sex, it's great. When I'm alone though, I have had to develop ways of hurting myself before hand, and this is how I usually do it now.
I plug in a flat iron and turn the temperature to a low setting (but it still gets pretty hot). I lay face-down on my bed or get on my hands and knees. I put the iron on my back. While it's heating up, I reach under and start masturbating. As the iron gets hotter and hotter, so do I. When it gets too hot, I quickly dump it off of me and put it on the floor. Then I have to act fast while the pain lingers. I lay on my back and masturbate as hard as I can until I orgasm or the pain dies down too much, whichever comes first. If I was unsuccessful, I repeat the iron again. But usually I orgasm the first try.
I have other methods of causing myself pain. I may write about them later if I feel up to it.
Thanks for reading.
PS. Don't feel sorry for me. My orgasms are extremely powerful and I actually enjoy being in pain. And my current boyfriend wouldn't hurt a fly but he's great at whipping me just right. We have a great sex life.