You shouldn't enter the opposite sex's restroom.
Rob is at an outdoor concert and has to go to the bathroom really badly.
Rob needs to find a restroom very quickly.
Rob waits for the men's bathroom, as difficult as it is for him to do that.
Rob can't find a place to go quickly, so he walks into the women's bathroom.
Rob gets to use the restroom, and he doesn't cause any problems for other people.
He finds that there are people trying to use the bathroom who are appalled by his presence, and he still doesn't get to use the bathroom.