This happened when I was 15 at school camp. I was staying in a cabin with two other boys. One afternoon, there was only james and I in the cabin. I had known james for years and had seen his cock when he was getting dressed before.
He was dressed in a t shirt and shorts but he had a hard on so he asked if he could let his dick out because the waistband hurt it. I said sure, and out cam a 7 inch monster. Seeing this gave me a hard on so I let my dick out as well. (James and I are both completely straight and have girlfriends but we often talk about sex).
Then he decided to have a shower, but he insisted on keeping the bathroom door open to allow me to go into the bathroom to brush my teeth etc. he still had a massive hard on and began to wash his whole body with soap, including his throbbing cock. He didn't jerk it although it was obvious he wanted to. So when he got out, I got in and we started talking about masturbation. This talk was making us both super horny so I asked him if I could wank myself and he said go for it. So I lubed it up with shampoo and started to move my hands up and down the six inch shaft.
James gave the occasional jerk to his own cock. He said that his pubic hair never stays down, even in the shower. He then got undressed again and got into the shower with me to prove it. Then I asked him if he would like me to jerk him off (something we had never done before) and he said okay. I grabbed his cock and put shampoo all over it. Then pumped up and down. He loved it and started to jerk my cock. we both sat down under the shower and jerked each other until we both cum on our chests. Soon we ran out of hot water and cleaned up. We never did this again and when our other cabin mate came back in he had no idea what we had done. The encounter still turns both me and James on.