This happened when I was much younger, and I have masturbated to this experience many, many times.
I grew up in a normal, loving, everyday family with two siblings, older brother and sister. Both my older brother and I have foreskin, which is not that common in the USA where we live. Growing up, mom always told us to pay special attention to keeping our privates clean during baths as she bathed us, inspecting the cleaning job herself. As we got older and took baths ourselves, she did not do inspections that often, but would just ask us if we had washed behind our foreskin to make sure it was 'fresh and clean' as she would say.
When I turned 14, I had been masturbating for a couple years, dry ejaculations at first, and then with semen shortly thereafter. My brother left for college behind my sister, so I was the only one living home at the time. I would masturbate often when mom was gone, and look at a Penthouse my friend had across the street, returning home to good privacy.
We lived in a multi story house with my room and bathroom on the lower level next to the laundry room, my parents on the up level. Mom still asked now and then about 'Did I clean behind my foreskin' and I would always tell her of course.
Dad had a week long business trip, leaving Sunday night. That night, just mom and me, after dinner and during my tub, she again asked for the millionth time if I had cleaned behind my foreskin and behind my ears and all that. I yelled in the tub 'Yes!' almost in a mad voice while in the tub. She was walking by the bathroom and checked in on me, and joked to me that I didn't need to yell. I said, sorry mom, you always ask me that, she said she knew and didn't mean to be on my case so much. I didn't give it a thought that I was totally naked in the soapy water with her in there.
She said she had to start a load of laundry and so there would not be much hot water left, but since I was almost done anyway, wasn't a big deal. She left and as I got out of the tub with a towel around me, I heard her start the washing machine. She returned into the bathroom completely naked, opened the cabinet door up, got out a towel and covered herself in it, told me we would be going to my Aunt's house in a few minutes, and left.
I was dumbstruck. I had seen her before around the house growing up, but never just her and I with her totally naked. She had very soft and thick, brown, pubic hair, in the shape is a large triangle. Her belly was white and stuck out a little bit just above her pubic hair. Her breasts were very saggy, maybe a b or c cup, with very nice red areolas. She must have tossed her clothes into the washer with the rest of the load. I got such a hard on, I immediatly masturbated, but did not come. A few minutes later, we spent the evening at my Aunt's house.
Two days later, it was bath time again for me in my downstairs bathroom, I couldn't get that vision out of my mind. Mom was cleaning up dinner, and said she would be downstairs in a minute. I took my bath and as I was drying off, she came in to check on me.
I don't know what got into me. Before she even said anything, I said 'Yes, I washed behind my foreskin'. She said, good boy. I asked her why she always asked that, she said when I got older, the girls I got to know would want me to be clean and smell good, not just there, but all over. I told her that made sense.
Without knowing what I was doing standing there wrapped in a towel, I asked her if she would 'inspect' my penis to make sure it passed inspection. She laughed and said there was no need for that, that I was old enough to take care of myself. I asked her please would she, and she said 'OK.'
I dropped my towel and she looked at my penis. I pulled the foreskin back and she looked it over, and then leaned forward to sort of smell it. She didn't touch it or anything, but she was so close to it, it was so exciting. She said it looked fine and clean and smelled good.
By this time, I had a raging hard on going, and precum started to ooz out. Mom asked if I rubbed my penis. I blurted out 'Never!' and she calmly said it was OK and to be honest. I finally said 'Yes, I do, it feels really good.'
She went on to explain that was natural, and to just be sure to clean my penis afterwards to keep it clean. She pulled my foreskin back and touched the precum with her finger, showing to me saying, this is all very natural. When you get done, be sure to wash all this and anything else that comes out with lots of soap. She then left to go back into the kitchen.
With the bathroom door wide open, I masturbated with my mom just up a flight of stairs away in the kitchen, probably knowing what I was doing. It felt so good and so free with the door open and no towel with her having just touched my erect penis. I imagined the sight of her nude and came so hard. I did clean up like she said. Nothing was ever said about it again.
I still think about that to this day, and have a great sex life, happily married for 15 years, and keep a very clean penis at all times.
Thanks mom, your the best!