Through the pitch-black night, the captain sees a light dead ahead on a collision course with his ship.
He sends a signal: "Change your course ten degrees east."
The light signals back: "Change your course ten degrees west."
Angry, the captain send: "I'm a navy captain! Change your course, sir!"
I'm a seaman, second class," comes the reply. "Change your course, sir."
Now the captain is furious, "I'm a battleship! I'm not changing course!"
There is one last reply. I'm a lighthouse. Your call."