A Man Rule Question

Sometimes, we men have to follow man rules and I ran across a man rule question the other day.
When working as a cashier at a local grocery store, I had a male customer.
As I was putting his groceries in the bags, I looked at him because he had purchased some booze. As I looked at this face to see what his aproximate age was and then looked down to grocery bags, I noticed the zipper to his pants was down.
Do I tell him?
If I tell him, I admitted that I looked at his crotch.
If I don't tell him, he will look the fool, especially to women who look down there.
As a man, what do you do?
Damn man rules.