The Grim Adventures of Billy and Mandy - Season 2 Episode 21 Terror of the Black Knight

After being impressed by Irwin's realistic armor at the medieval fair, Billy wishes for a fancy armor too. Grim gives him the "Cursed Suit of the Black Knight". When Billy needs to go to the bathroom, the curse is revealed to be that the armor cannot be taken off until the person wearing it beats someone in a competition. Billy desperately tries to defeat other people at various contests, he but fails to come out victorious. He defeats Mandy at a breakdance contest in which Mandy decided not to participate, but he does not need to go to the bathroom anymore.