Skeletons hate old people.
They hate them so much they setup up an elaborate court-room drama just to screw with this old guy. They even rented a bat from the vampires, and one poor skeleton sacrificed his head just for added shock value.
The coffin as the jury box is a nice touch, though it being nearly square means it's only suited for SpongeBob SquarePants, and frankly, he doesn't have a skeleton.
What's this old guys crime? Not drinking enough milk and bitterly complaining about the aches in his bones. Again, skeletons just really, really hate old folks.