On the Front: A photo of a woodchuck yelling, with his paw in the air.
Along with the words:
OH, YEAH? WELL, MY DAD WOULD CHUCK MORE WOOD THAN YOUR DAD WOULD CHUCK, EVEN IF YOUR DAD COULD CHUCK WOOD. WHICH I DOUBT!
The reaction: Much hilarity and mirth (and some snorting). You don't even need anything written on the inside, really.