Pain for Pleasure
A woman once jerked me off using nothing but her long fingernails. She wasn't scratching me, only digging in just enough to move the skin on my cock up and down.
It was MADDENING!
Her hands were making my cock feel so good that I wanted to cum, but the small jolts of pain from her nails kept knocking me off track. I kept getting close to cumming, but each time my cock would start to spasm, her nails would dig in just a little more and cut my orgasm off. She kept it up for a good 20 minutes before finally letting me spurt.
I've tried it again since then but:
a) I don't have long fingernails, and
b) it's difficult for me to dig in enough to cause the sensations without backing off.
I do remember that it was one powerful orgasm, when it finally did come around.