There was a little boy named Johnny who used to hang out at the local corner market. The owner didn't know what Johnny's problem was, but the boys would constantly tease him.
They would always comment that he was two bricks shy of a load, or two pickles short of a barrel. To prove it, sometimes they would offer Johnny his choice between a nickel (5 cents) and a dime (10 cents) and John would always take the nickel -- they said, because it was bigger.
One day after John grabbed the nickel, the store owner took him aside and said "Johnny, those boys are making fun of you. They think you don't know the dime is worth more than the nickel.  Are you grabbing the nickel because it's bigger, or what?"
Slowly, Johnny turned toward the store owner and a big grin appeared on his face and Johnny said, "Well, if I took the dime, they'd stop doing it, and so far I have saved $20!"