The underside of my penis is super sensitive. I am cut, but I still have my frenulum attached. I get more pleasure just rubbing it rather then stroking.
The issue I had and still have is when I was being examined, the doctor would examine my penis thoroughly and I would always have an erection. As the doctor would hold the base of my penis, with his other hand palpate the shaft and when he got to the head of my penis he would just rub and feel the underside of my penis which would make me ejaculate.
This sensation would drive me crazy, and it was also very embarrassing since I would ejaculate during the exam and my mother watching the entire exam. The doctor would even comment to my mother how sensitive my penis was and he would point out my sensitive frenulum to her.
If you read my past stories, my mother did home inspection on me and would tease my frenulum during these inspection and I would ejaculate. It didn't take me long to achieve an orgasm and if she would do it right and took her time, I would produce a lot of pre-cum.
When I got older and moved away, I have always enjoyed others playing with my frenulum and teasing the underside of my penis, even in my own time, I don't “masturbate” I normally just rub and tease my frenulum until I ejaculate. The sensation I get from it is super great.
Many years back I discovered e-stim and poppers and that is a great way to have my frenulum teased and especially doing poppers, it teases me and it builds up the sensation so when I do ejaculate, I have an amazing orgasm.