When I was in the Army, there was a guy in my unit who was a trained mechanic. He was a friendly and cheerful guy and he was always ready to help out when anyone needed work on their POV. The mechanic had a friend who was kind of a hick but who also knew a lot about auto mechanics. He helped the mechanic when he worked on cars. Everyone liked these guys.
After a while it got to be obvious that the mechanic and his friend were a couple, as they say. You wouldn't think they were gay or anything from the way they acted or behaved individually but you could tell from the way they acted when they were together that there was something going on between them. This was long before don't ask don't tell but everyone just accepted that they had a relationship and no one said anything about it. Except once someone said something about it to the mechanic and the mechanic beat the shit out of him.
One day I had pulled an all-night duty and I had the day off. After the sergeant had come through to inspect, I undressed, grabbed a towel and went to take a shower. To get to the shower you had to walk through the latrine. When I went in the latrine I could hear the water going in the shower. I was kind of disappointed because I'd been thinking I'd have the shower all to myself and I'd been planning on a private jerk-off session.
When I got to the doorway to the shower room I stopped cold. The mechanic and his friend were in the shower doing something that can't be described here.
At first they were having so much fun they didn't notice me standing in the doorway and I watched them for a few moments. I'd looked at some gay porn once and it didn't do anything for me, it just made me feel uncomfortable. But seeing my buddies going at it like crazy in the shower really turned me on for some reason.
When they realized I was standing in the doorway they disengaged and stood glaring at me for a few seconds. All at once all three of us burst out laughing. I had a massive hard-on.
I grabbed my dick and started masturbating and they went back to doing what they'd been doing. I worked up to a huge orgasm watching them.
Of course I knew that they would never say anything about the incident in the shower and they knew I wouldn't either.
I've relived that incident so many times while masturbating.