Who's being pranked?

There's a little fellow named Junior who hangs out at the local grocery store. The manager doesn't know what Junior's problem is, but the boys like to tease him. They say he is two bricks short of a load, or two pickles shy of a barrel.

To prove it, sometimes the boys offer Junior his choice between a nickel and a dime. He always takes the nickel, they say, because it's bigger.

One day after Junior grabbed the nickel, the store manager got him off to one side and said, "Junior, 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?"

Junior grins and says, "Well, if I took the dime, they'd stop doing it, and so far I've made $20!"