For losers with the soap gene: eat an entire bunch of raw cilantro. For everyone else the league substitutes their most-hated food in quantity. Tailoring the menu to the loser's specific weakness is what separates artisanal leagues from amateurs.
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.
Seen in the wild: reddit.com