Aristotle Onassis (1906-1975) was a Greek millionaire with very specific tastes. He owned fleets of ships, and did a lot of business on his own yacht, the Christina.
There was a bathroom off of Onassis's office there. The millionaire decided to install a one-way mirror on the bathroom door so that he could spy on people while he busted grumpies. And so it was done.
But the first time that Onassis went in the bathroom to sit down, he was surprised to find that he was looking at a reflection of himself. Wait a minute—
The mirror had been installed backwards . . . and the people in his office could see him!