The league writes the poem; the loser performs it at a real poetry slam, receiving the text only 30 minutes before going on stage. Cold-reading your friends' most unhinged verse to an audience of sincere poets is a specific kind of terror. Snaps are earned, somehow, every time.
Budget note: this one costs nothing but dignity, which makes it a strong pick for leagues that would rather spend the pot on the champion than on the loser's downfall.