I know the great feeling.
Whenever I am in the men's room and a man walks in after me, hesitates, and says "I thought this was the men's room" then they walk back out and see the sign, and realize I was male, and they just called me a woman, they usually do not come back in, in the fear that I am offended.
When I am in the ladie's room, woman will sometimes, but not usually, walk right in as if I am supposed to be there.
By the way, I am not a creeper, I am a janitor at a grocery store... LOL