There's a little fellow named Junior who hangs out at Tim Alley's 
Grocery Store. The owner Tim doesn't know what Junior's 
problem is, but the boys like to tease him. They say he is two 
bricks shy of a load, or two pickles shy of a barrel. To prove it, 
sometimes they 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, Tim 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 said, "Well, if I took the dime, they'd quit doing it!"