When I was 13 or so, the neighborhood boys and I would video games or baseball or something else in the summer, and the looser would have to loose his shirt and sit in front of the window air-conditioner.
One day, I decided to up the bet when a friend (Matt) and I were playing. We were going to play a board game and we determined that the loser would have to loose all his clothing and sit in an air-conditioned room with a fan at his genitals. Matt and I had seen each other nude a few times when changing to go swimming or something, but we had never had to sit for long periods of time in front of the other without a stitch. We debated back and forth about the time we would have to sit naked in front of the other, and we finally decided upon 3 minutes.
The game commenced, and I was doing fairly well, but things took a turn for the worse and I lost the game. Matt and I went to his room, while I picked up the pieces of the game. When I got to his room, he had set a fan in a corner of the room. I handed him my watch so that he could time the penalty, and I stripped. I was very self-conscious as I took off my underwear, but I knew we had a bet, and I was going to fulfill my part of it.
I took off my clothes and sat down at the fan. Matt was fascinated by my genitals, as he was the first time he had seen them. I had gone through puberty and he had not. As I sat behind the fan, he kept staring at my genitals. I had an erection, and I began to masturbate. He was always fascinated by watching someone masturbate, so he encouraged me to continue. Matt put the watch away, as I was going to need more than the 3 minutes of the bet to cum. I told him when I was about to cum, and he watched with his eyes glued to my genitals. After I had fulfilled the bet, I put my clothes back on. We played several other games, some with my loosing and some with his loosing. He saw me masturbate several times after that first time, but he never masturbated in front of me, probably because he couldn't ejaculate. Yet, that first time is quite memorable.