Double Standards in the Bathroom

Why is it more "okay" for a woman to use a men's public bathroom and it would be time to call the cops if a man used a woman's?

I was in our building bathroom, working something out and an older lady came into the bathroom, checked the stalls (pulled on the door handle to my stall a good five or six times), peered in the shower area and then left.

What the fuck? What the fuck are you doing in the men's room?

Rules For Proper Bathroom Etiquette