The latest column by John Stossel  (of ABC News) is splendid. I especially like this observation:
How many times have you paid $1 for a cup of coffee and after the clerk said, "thank you," you responded, "thank you"?
There’s a wealth of economics wisdom in the weird double thank-you
moment. Why does it happen? Because you want the coffee more than the
buck, and the store wants the buck more than the coffee. Both of you