When I was 13 or so, at the height of my teenage horniness, I had an experience happen that was totally unexpected. I was watching TV at my friend Joe's house. Joe was my age and also was a pretty horny kid. We talked about sex often, and he liked to show off his body--walking around in his underwear, mooning everybody, etc. But I never thought anything would happen between us because the few times I had hinted at playing around, he had seemed weirded out about it. I had several other boys my age that I was playing around with sexually, so I was okay with nothing happening with Joe, although I had always secretly hoped something would happen.
Anyway, this night Joe and I were sitting on his couch watching TV. His parents were gone somewhere for a few hours, and his older brother was sitting on the floor in front of us. We weren't even watching porn or anything like that, but at that age you think of sex constantly, and pretty soon as usual our conversation headed in that direction. Joe's brother was really into the TV (or at least was pretending to be) and seemed totally oblivious to what we were talking about. We started talking about our penises and how big they were normally, when erect, etc. Then we started saying stuff like 'I'll bet mine is bigger than yours', and pretty soon we were measuring our own penises through our jeans, and then holding our hands up together to compare measurements. We did this several times, and we both were getting boners along the way. From the measurements it looked like we had the same size penises, and Joe said 'I don't believe you' and reached over and felt around the crotch of my jeans until he found my penis and measured it himself. I was in shock, thinking that that would never happen with Joe. But I quickly recovered and reached over to feel his penis, which did turn out to be the same size as mine. We measured each other's cocks several more times, and were both about to burst from horniness. His brother was still totally ignoring us, so we then gave up all pretenses and progressed to rubbing each other's cocks through our jeans, slowly at first. I wanted nothing more than to rip off our clothes since rubbing through jeans is less than ideal, but with his brother sitting right there this would have to do. It felt great, and it was all that either of us could do to keep quiet as we squirmed around on the couch as we fondled each other. Our pace soon quickened, and right when I was nearing the point of no return, we could hear the garage door begin to open. Their parents were home. Joe had been close to orgasm as well, with his eyes squeezed tightly shut and his breathing quickening, but his eyes flew open at the sound. He jumped up guiltily and began to walk towards the kitchen, then apparently thought better of it and ran back over to the couch and started rubbing my cock again. Maybe he wanted to give me an orgasm before his parents walked in. But soon they came inside and we sat there pretending like nothing was going on, covering up our raging hardons.
We never again did anything sexual together, even though we were friends for many more years. I always wondered what would have happened if his parents hadn't come home. Would that have progressed into something more? Who knows. But it was a fun and unexpected experience anyway.