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 yours, ten degrees west."
Angry, the captain sends: "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's one last reply. "I'm a lighthouse. Your call."