When I was 15 and in 10th grade, my bio class went on a field trip to a national park. We stayed in cabins, four people per cabin. I was with Max, Jon, and Sam. We were all good friends so we didn't mind changing or showering or using the bathroom in front of each other, but it was expected that nothing sexual would occur.
On the second night of the trip, Jon and Sam were off doing some special star-gazing thing with my teacher, but Max and I stayed in the cabin. Max went off to take a shower leaving me all alone in the sleeping room. I was bored so I asked if I could come into the bathroom and chat while Max was showering. He agreed so I sat on the toilet as he showered and we started talking about school. This led to the girl Max is really into, Nikki. The conversation started getting really sexual and my dick started to harden. Then all of a sudden Max says: 'Hey, Dan, mind if I jerk off? 'I was silent, and he took the silence as a yes. I could start to hear my friend having fun in there, so I decided I wanted in on the action. I said: 'You mind if I join?' He responds: 'You could've just told me you wanted to watch.' With that he flung the curtain open, exposing his naked body with an eight inch cock in his right hand. We both started laughing. As he continued stroking, I stripped down and got in too. Now the two of us were squeezed into one shower jerking off.
After a min of not talking, he faced me, looked me in the eye and said 'Ready or not here I cum!'
He came all over my wet stomach, and his cum fell down to my own cock. He took a hold of my dick and started to help me. I came a minute later thanks to his wonderful handjob. We finished cleaning up and then exited the shower and hung out naked until our roommates came back.
It was a wonderful trip.