So he's under a rest.
Emewafwawa tells this joke to his victims to break their morale, The picture represents someone who was told this joke by Emewafwawa and went so insane that he actually dressed up as the man and put a rest on his head, and then danced around the room going "I'm under a reeee-eeest! I'm under a reeee-eeeeest!" in a very child-like manner. Odd.