I recently used "Hello, I must be going" as sung by Groucho Marx in the movie "Animal Crackers"--

Hello, I must be going,
I'm sad to say I really must be going;
I'll stay a week or two,
I'll stay the Summer through;
But now I say to you,
I must be [drop voice as low as you can go] go-ing.

I generally introduce this as part of the philosophy of the great philosopher, Marx. It's amazing how few people get it until the song has proceeded into its middle.