Whose loo is it?

Guess you can attribute this to our quirky senses of humor at work--work in a lab with a bunch of ladies and one lone fellow. He laid claim to one of the restrooms and calls it "his", the "ladies" room being the one "back there in the corner." (All in jest, mind you, but it is a running gag.) How can you NOT try to take the mickey out of that? So, one day, when we were bored...this happened.