We have a tiny downstairs bathroom: you can literally wash your hands in the sink while sitting on the toilet. In an attempt to make it look bigger, my wife put a large mirror on the wall above the toilet.
She didn't appreciate that it meant a guy would staring at his own junk while urinating standing up.
This happened just before a party we were throwing (it was one of the ways my wife wanted to spruce up our house).
I put a notice up that "objects in this mirror are larger than they appear".