Locker rooms give a false impression of size because it seems to me, big guys tend to strut around naked while small guys tend to cover up us quick as possible. I include myself as small because my flacid cock is only around 2 inches long and looks even smaller thanks too it's girth.
There was one time though when I was at my slimmest (40 pounds less than now) and i'd just been in a hotel pool fooling with my GF to the point where we'd decided we should go back to our room and fuck. I found myself showering in the locker room with a fat 5" semi, I walked around naked and confident that day, specially around one averagely hung looking guy had been unable to keep his eyes of my GF in the pool. Had a lot of fun when I got back to the room too...