When I was 13 years old a 14-year-old friend of mine came over to my house to spend the night. When night finally arrived, my friend went to the bathroom to prepare for bed. He returned with a couple of tissues and asked me whether I 'wanted to'. I didn't know what he meant, so I asked him to explain. He simply said 'you know', and I finally understood. I had always wanted to masturbate with a friend, so I said okay.
My friend had brought an adult magazine with him, so we laid down on my waterbed, covered our torsos with blankets and took out our penises. My friend grabbed his penis through his blanket to show me how long it was, and I did the same. Mine was like two inches shorter than his, and I really wanted to see what his penis looked like underneath the blanket but I was too afraid to ask.
We started masturbating to the magazine, but once we began I was most interested in seeing my friend jerking off. I pretended to be interested in the magazine but I spent more time looking at the bulge under his blanket than at the girl in the magazine. After we both came, my friend lifted his blanket just a bit to show me the glob of semen on his belly.
It was the first time I had seen so much semen. At that age I was only able to produce a few drops of clear precum, so I was really turned on by the way his semen looked on his belly. The glob of semen was thick and about the diameter of a quarter, and it had a kind of bumpy appearance. I felt like I wanted to lick it off and eat it, but I didn't dare ask.
While he was showing me the semen on his belly I tried to peek beneath the blanket to see what his penis looked like. I had always wanted to look at a friend's penis, and I was turned on by the idea of looking at his penis since it was longer than mine. I managed to see the base of my friend's penis, but he caught me looking and asked me 'what are you looking at?' I said 'nothing' and stopped staring at it so much.
He then wiped the semen off his belly and we threw the tissues in the trash and went to sleep. I regretted not being able to see his penis, but it was still a pretty fun evening.
By the way, this friend later told me a story about the time when he masturbated under a blanket in the back seat of his car while his parents were sitting in front and his sister was sitting next to him. I would never feel comfortable doing that with my family in the car, but it was kind of exciting to imagine him doing that under a blanket.
We never did masturbate together again, but it's something I'll never forget.