Rule #1 If a man's fly is open, that is his problem. You didn't see anything.

This is a very important rule. There is not much need to expound on this. For some unexplainable reason the eye is naturally drawn to an open fly, but we are men and there is no acceptable reason for one man to ever look at another man's crotch.
It is ok to spot an open fly. They are as common as metrosexuals in the GAP. However, as a man, you would never let another man know that there are windows in his laptop.