This happened when a friend of mine and I were about 15. He was spending the night as we often did at each other house over the weekends. This time it was at my house.
We were staying in my sister's old room - she had moved out and my parents hadn't gotten around to making it their room yet. Seeing as it was the master bedroom it had its own bathroom.
We played video games, watched movies, went swimming in the pool we had etc - typical stuff just hanging out. Later that night were getting ready go to sleep - my friend wanted to take a shower- so he went in started the water and got in. About 5 minutes he called out said he forgot to grab a towel. I went and got one from the hall closet and walked in and left it on the counter. I would see through the steam covered glass door that he was stroking his cock. From the looks of it bigger than mine.
For some reason, as a prank, I turned on the cold water at the sink - this of course gave the shower a jolt of hot water - ha ha. My friend called me a few names - along with complaining, 'damn that water is hot.' My thought - hey the water is hot - ok. I went and got a pitcher from the kitchen - filled it with cold ice water let it sit for a few minutes - then went in to the master bathroom and poured it over the top of the shower stall - so much for being hot because of the hot water!
The next thing you know he said something to the effect - 'it's a good thing I'm not in there because if I would were I'd be paying for that prank!' I thought about it in less than a minute - I striped down, opened the shower door and climbed in. My friend was standing there with his back to me stroking his cock. I said well 'I'm here - how do you think you're going to make me pay?' He turned around still stroking his cock - put his hand other hand on my cock and started to stroke me. It felt awesome to say the least. I reached for his cock in return and began stroking his cock with him. A few minutes later he removed his hand from his cock and put it on my shoulder and more or less pressed downward wanting me to be on my knees.
I took the hint and right there in front of my face, was my friend's cock with my hand stroking him. By then he had his hands on both my shoulders ... and he was fucking my hand. He shot his load after about 3 minutes all over my face ... and yes some of it ended up in my mouth.
We got out of the shower afterwards and went to sleep - we both decided to sleep nude. I woke up a few hours later with his cock rubbing against my lips - I opened my eyes to see him straddled over my face I was looking up at his cock and balls, but that is another story as is a few weeks later when my friend and his brother both spent the night and all three of us ended stroking together and each other.