If I could go back to shorts for a minute, and leave Wolf on the psychoanalyst’s couch for later… Shorts on a man might be a tzniut problem, if it would cause the surrounding population to gawk. Tzniut for men is – or should be – treated similarly as for women. Maybe there aren’t as many areas that men halachically have to cover up, but calling attention to one’s physical attributes is inappropriate in most settings.
On the other hand, IMHO, at the beach (if one were to go to the beach) one were to call more attention to oneself dressed in a white shirt, black pants and a hat (yes, I am aware of the incongruity of the beach and black hat examples!)
I guess, based on my theory then, shorts on a well-toned, tan young guy would be assur, but on a fat, hairy, old white guy they’d be perfectly OK….?