All my dude friends, up until about 24, I saw naked. But newer friends after that I don't think I've seen any of them naked. Experience for playing sports, I guess. Never seen any guy with a full erection. But there's been a few times where guys have gone out streaking for one reason or another. Running naked for me invites at least a semi-. I can't help it. And frankly it felt great having a little bouncing weight while I ran. Friends would often get a little hard when we were being stupid, streaking, trying to embarrass each other or the people we were being stupid around.
A group of us were out at a lake during a summer bbq, girls and guys. We were playing bags in an elimination game. Our buddy Rob bet he'd beat the girls and would take a dare if he lost. He lost. So they made him get naked and skinny dip that night. The rest of us dudes said we'd get in naked too if the girls did it, they agreed so we all got naked. Couple of boners during that one too. Most of us got laid that night too.