When I was i the Marines, I'd cut the liners from my running shorts and watch the Marines checking out my penis flopping completely out of my shorts, flopping around and getting fully erect.
I would have liked to see him cumming with his dick out with the cars driving by or standing up (and if worked up enough) cumming in those shorts like the guy wearing long pants in the adult bookstore video.
I remember as a teen seeing a man like this with a bulge in his shorts. I couldn't stop staring even when he exposed his cock. I went home and masturbated wishing I had sucked his cock.