Soon after we were married my wife's sister was on a visit. We had drunk some wine and the conversation got around to sex. My sister-in-law had not had a steady boyfriend up to this point. My wife asked if she had gone all the way with a boy and she replied "no" and added that she had not even seen a man's penis in the flesh which she said she longed to do. I think my wife was feeling sorry for her sister and suggested that I show her my penis if I promised to keep my distance. I couldn't believe my luck. Her sister's eyes lit up and she gasped with excitement as I stood up and started to undo my trousers.
I dropped my trousers and asked if she was ready for me to pull down my underpants. She didn't hesitate to say yes. I pulled down my underpants and my cock was semi hard. My sister-in-law focussed her eyes on my cock without speaking. The situation was getting me excited too and my cock started getting harder until fully erect as she watched the whole erection process. "I want to touch it" she said as she looked to my wife for permission. I prayed for my wife to give her the permission which thankfully she did, telling her that she could only have a little touch. I moved closer to her for her to touch my cock. She actually held it for a while and even moved my foreskin up and down a couple of times. The sensation for me was fantastic and she said it was the most erotic thing she had experienced.
My wife said " ok, show over" but her sister was so excited that she said she wanted to touch it more. Before my wife could stop her she put her hand back around my cock and played with it all over, including around my balls . She remarked how hard and warm it now felt. I was now getting very excited by all this attention to my cock. I felt my cock throbbing as she caressed it and I knew I would soon cum if she didn't stop. I could have pulled away and ended this exhibition but I thought, when would I ever get another chance to have my cock played with by my sister-in-law with my wife looking on? My wife was now just sitting and watching and seemed to be getting pleasure from watching her sister experiencing fun with my cock.
As she fondled and stroked my cock she asked if I was having an orgasm as she noticed I was breathing heavily and my penis was now getting quite wet. I explained the wet was just pre cum but warned her that this was just the start as I was about to fully ejaculate and was now unable to stop it as my cock started twitching and throbbing in her hand. Then came the full force of my ejaculation as she continued holding my pulsating cock while gasping with amazement at the amount of semen which shot out in several spurts. She yelled "oh my !" with the excitement of this erotic episode during which she had not only seen and touched my erect cock but had also got me so aroused that I couldn't stop myself from cumming. I told her that the ejaculation was involuntary, it was just as a result of the erotic situation. She told me not to apologise as she actually hoped it would happen so she could watch the full process, but she had felt too embarassed to ask me to masturbate to orgasm.
Since that occasion I had hoped my sister-in-law may ask for a repeat show on her subsequent visits but, alas, she soon got her own boyfriend and husband and never referred to it again. I sometimes still think about it, though, when I masturbate.