When I was a youngster, my mother used to pull down on the loose skin of my penis whenever she gave me a bath, or even on any occasion when I happened to be naked around her. She called it 'skinning back'.
It stopped after I was about 5-6 years old but I always remembered not just her doing it, but also seeing her do it to my brothers and cousins when she was bathing or changing their diapers.
When I was 17, I finally asked her why she did it. She explained that after I was circumcised, the remaining skin would sometimes tend to stick to the head of my penis and the doctor instructed her to break it loose whenever it happened. She went on to tell me that sometimes it would bleed, so instead of waiting for that, she 'skinned back' my penis as a preventative measure every time she saw it.
She also said that I probably do it all the time to myself in the shower. I had to think about this for a second, because I didn't think I had any skin left to stick. I mentioned this to my mother and she became curious, and asked if I wouldn't mind letting her see. I was apprehensive because I hadn't let her see my penis since I was much younger, but she calmly insisted, so I took my penis out of my pants and let her look at it.
At this point, I don't know why, but I had an erection. She told me not to worry about it because it was a normal thing. She grabbed my penis and pulled the skin forward so that it bunched around the edge of my glans, explaining that it looked like that (bunched up) when I was younger. She then ran a fingernail around the corona and said that the skin would stick there. Finally, she skinned back my penis, pushing the bunched up skin all the way back to the base and held it there. My penis twitched a few times under the pressure and she let it go, surprised.
When she let go, she looked at it laughed and said that twitching never used to happen before. She then asked if it hurt when she skinned back my penis. I told her it wasn't exactly a hurt feeling. She said that she used to try to be as gentle as possible, but sometimes if it got stuck, it would snap back when the stuck part gave way. Before I could say another word, she casually bunched up the skin again. This time, she pinched the skin against my glans with one hand, and with the other tried to skin it back, so it put tension on the skin, but didn't move. She was demonstrating what happened when it got stuck. Then suddenly, she released the pinch hold from my glans and skinned back my penis with a snap.
This time it hurt, and I jumped back and yelped. My penis started twitching again, this time very animatedly. Instictively, my mom wrapped her hand around it as if to soothe me, and said she was sorry, she didn't mean to hurt my penis. To my horror, the sudden snap and then her holding it triggered the spasms of orgasm, and I grabbed my penis away from her hand to stuff it away, but it was too late, my semen started to burst out.
At the time, I was mortified, but she had no real reaction at all, she just watched it happen.
I was embarassed for a long time, but after that, mom made light of the whole situation and we laughed about it.
I hate to say it, but I still masturbate over it, even though I was so mortified at the time.
About a year later, she accidentally saw me in the bathroom after a shower. Again I was embarrassed and she teased that I should just get over it and she'd help me by giving me a bath one day, she'd even skin back my penis and wash it. I wish I had the nerve to let her do it.