One time 4 of us went camping at a campground. It was me, my wife, her sister and her husband. When we got there, me and my brother-in-law were a little sweaty and decided to go have a shower. We went down to the showers and it was one big shower room. It was going to be awkward getting naked in front of him because we had never been naked in front of each other. I began to think how awkward it will be showering in front him and began to worry about what he might think if I suddenly get an erection for some reason because I won't be able to hide it. We both undressed and began to shower. My worrying was for nothing and it really wasn't awkward like I thought it might be. It was just the 2 of us in there and we were talking like we normally do. Towards the end of our shower who is at the entrance to the shower room but both our wives. They begin to talk to us as we were showering. They were in clothes but us 2 guys were naked and our wives were looking at each other's naked husband and not making any effort to quickly leave. It was getting a little awkward now because I wasn't expecting my sister-in-law to see me this way and for my wife to see her husband the same way. It got even more awkward for me when the thing I worried about happening in front of her husband began to happen. I began to get an erection and decided to ignore it was happening and just kept showering. I think they all noticed but didn't say anything. Our wives stayed until we were done and all 4 of us walked back to our camp site.
I never found out if our wives planned this whole shower thing just to see us naked or if it just accidentally happened and they both just decided to take full advantage of the situation.