This just happened this morning and I'm still grinning about it.
With my holidays almost over and my wife already back at work I decided it was time to give the pool a thorough clean. I worked most of the morning to the loud thumping beat of the Ramones and by 11am the water was sparkling and I had sweat running off me. With the water looking so good and me being so hot, I stripped off and dived straight in. I knew my 85 year old mother in law was due to visit that day, but she had told my wife she would not arrive in town until well into the afternoon.
The sun was shining, the water was great and without thought I soon had a hard-on that would please a porn star. I got out of the pool, switched the cd player over to some easy listening and lay back on a sun lounger. Almost absent mindedly I started stroking myself and enjoyed the feeling of the sun on my cock. I'm not sure how much time passed, I was almost in a sleepy trance, but just as I felt the familiar stirings of an orgasm I heard my mother-in-laws voice saying, 'Barbara (my wife) should take care of that for you, I must have words with her.' I jumped up, my penis swinging straight out before me, and she said, 'Don't point that thing at me, make it go down.' I stupidly said that there was only one way to make it go away now, and the mother-in-law said, 'Well are you happy to finish it with me here or do you want me to go away for a little while.'
I don't know what came over me, a little bit of bravado perhaps, but I just smiled and started to masturbate again. My mother in law watched intently until I came in great spurts of creamy white cum. I then returned to normal and started to apologise, but my dear mother in law told me not to worry, she'd been married 48 years and knew that sometimes men had to do these things. I kissed her on the cheek and told her I had the best mother in law in the world, and then asked her not to tell my wife. She promised not to tell Barbara, but also made me promise to be more discreet in future.