I grew up in a small town, and lots of family lived nearby. We had a great house, the previous owners had converted an extension into a self-contained guest apartment with a lounge/bedroom area and a toilet/shower. The best part was that my folks did not often have people over and it was given to me as a games/video room. My own space, fabulous.
I loved to head there early in the morning, because the noise did not disturb the others, and play games on my console. I got used to waiting until every one had gone to work, and then had a shower, got ready for college and headed out. That shower, in my 'private' shower was the place that I did most of my masturbation. I got all soaped up, and then imagined the girls at college, ......'s friends, neighbours, relatives, pop stars etc while I gave my uncut cock a really good wash. At that time, it did not take long, everything was sensitive.
One day, unknown to me, my aunt had called around to collect some stuff for a local car boot sale. The boxes were in my video room, and the aunt walked in unaware that I was having a shower. From the bedsit room, she had a clear view of the shower, and as she walked across the floor, I was side on to her, totally unaware, and having the normal daily wank.
I realised something was going on, when I heard a small cough. Looking around, and my aunt was sat on the bed, looking at me. 'Sorry', she said, 'I guess that you weren't expecting me today'. I can remember making some kind of mumbled apology, my face was as red as a beetroot, and I was covering myself up with my hands. My aunt laughed, 'Don't worry, it is perfectly normal and healthy, but it is not good to stop in the middle. My boys do it all the time, it is no biggy, why don't you finish off and then we can have a coffee together'. I asked if she was planning on waiting in the house, and she said something like 'I think I might just rest here a while, there is a great view and I am sure that you will enjoy it more with an audience. Who are you thinking about in there?' I probably came out with some lame excuse about some girl I knew, and I do remember her laughing and saying that she hoped it would be her turn next. She then said that I should hurry up, she had to be off soon, and did not want to miss the end of the show. I was horrified and excited in equal measure, and managed to produce a nice big load, which got a clap from her.
Needless to say, the coffee was a bit embarassing, but she was really good about it. Never told my parents, and it has remained our little joke to this day