I did it once with a male in a remote outdoor location–both of us sitting on a sheet. I'd seen his flaccid penis previously, hanging big with lots of loose skin; but his erection was really big–very thick–and mine, well, just the opposite. It was like a cucumber versus a cheese stick. He was the one that had earlier proposed the connection, perhaps sensing a mutual attraction; but his surprisingly attractive bare buttocks, and not his penis, had actually caught my attention and raised my pulse rate.
Manipulating each other at the same time turned out to be confusing to me, so I finally released his penis so we could both focus on one. He used his thumb and forefinger to manipulate my glans until semen began welling out, but there wasn't any real spurting, and my orgasm was only mild. The lack of spurting was ironic because I had seen him initially adjust his body position, I think, to avoid getting sprayed in the face.
Then I tried vigorously working his erection using an entire handwrap, but my arm tired. Grasping his very bulky, heavy organ felt very strange and unsatisfying to me and I think we just needed some practice together. At least he was able to see me emit some semen, which he seemed to enjoy.