My girlfriend, some friends, and I went berry picking two weeks ago. While we were waiting for the wagon that will carry us to the berry fields, a middle-aged man with his wife was attempting his best shot at humour. "What will happen when the wagon comes? They'll paint it?," he said. The thought of some bizarre need of painting a wagon prior to a ride was a bit funny to me, to I smiled. The man noticed my smile:

-- Do you understand my joke?
-- Well, I think I do.
-- Do you know what reference I am making? It was a movie called "Paint My Wagon," or something. What was it?
-- I... I don't remember. (Actually, he just lost me there.)
-- You don't understand my joke do you. (Then he speaks to his wife.) Do you know what I'm talking about?
-- Yes, I do., she said.
-- Oh, so you understand my joke? That guy here doesn't understand my joke. He doesn't know what I'm talking about.

And then he kept complaining about how I didn't understand his joke. The wait for the wagon was becoming as long as waiting for a bus under the rain. I just had to say something to bring all this to an end. "Well, I'm sorry, sir. I was smiling just to make you feel better, because even your wife understood your joke and didn't think it was funny."

There. That worked -- didn't hear a single word after.

I think he was referring to this movie:
http://en.wikipedia.org/wiki/Paint_Your_Wagon_%28film%29