A couple that come to mind.
When I was younger one of the group of guys I hung out with was nicknamed Whopper, and yes he had a whopper. It must have been 6/7 inches soft and thick. He was so proud of it he couldn't keep it in his pants, it was always out with him stroking it or slapping it around, but his favorite was the helicopter twirl. Strange thing was I never saw it get hard, which I was curious about. One night my best friend suggests we go streaking, there were about 6 or 7 of us, so off come the clothes and we're running through the park. Whopper decides it would be funny to start tackling guys and dry humping them, everyone got a turn, even if we had to help tackle them. Them someone yells lets tackle Jim and Whopper can slap him in the face. So we tackle Jim and Whopper straddles his face and starts slapping him with his dick, everyone's laughing and Jim's laughing and Whopper pops his dick right in his mouth, and it's even funnier. Now it's my turn, so I get held down and as Whopper straddles my face I yell if you get that thing near my face I'll bite it off. I got a few slaps but not near the mouth. Everyone got a turn and half the guys ended up with Whoppers cock in their mouth, and that was the end of it. The funny part was I had been jacking off and sucking my best friends cock for a couple years, and loved doing it. I also had often wondered how big Whopper's cock would get when it was hard, and how big a load he shot. But he was a talker and never wanted to take the chance.
Another time was in the Army. One of the guys in the unit had a TV in his room, that was a big deal back then and says there's a Stevie Nicks concert on tonight, want to come over and watch it? Hell yes, I'll bring the beer. So I get there before the show starts and we're having a few, and we're getting buzzed and he says I got some pictures of my wife, want to see them. Sure, why not. They turn out to be nudes, various poses, some playing with herself. Half way through the concert we're buzzed and he starts talking about how hot Stevie Nicks is and how he'd like to fuck her, etc. A couple more beers and he's bombed and lays back on his bunk and I notice he's rubbing his cock, and soon just pulls it out. I'm not sure if I should stay or leave, the last thing you want is to be labeled a fag, and I can't tell if he realizes I'm in the room. Well I decided to stay and see what happens, pretty soon his pants are mid thigh and he's stroking his cock and playing with his balls. It didn't take long and he grunts and cums all over his chest and stomach, and rolls over and goes to sleep. I quietly let myself out and went back to my room and jacked off thinking about what just happened. The next day he says, that was a great concert, but I must have fell asleep before the end.