There is no easy way to tell another man, a stranger, that his fly is down.
Today I tried the "Fraternity of Males" tone: light, but not too light; jocular, but not too jocular; quietly discreet.
It was not a success. No matter how much he may have appreciated my gesture later in the day while talking to his boss' attractive secretary, he still still looked at me as if to say, "Faaaaaaaaaaaag."
I remember when C and I were kids we'd sit in the mall on a bench snapping our fingers in front of our denimed laps. When someone walking by chanced to investigate what was making the snapping sound, only to discover it was our fingers before our balls, we'd give them the dirtiest look possible. Sometimes even 'tsk tsk' them, as if to say, "Keep stepping, you sick Peder-ass!"
Ah, what a beautiful, misspent youth!