The loser performs solo karaoke at a real bar on a busy Saturday night, singing songs the league picks, often deliberately out of their range or repeated back-to-back. Costume add-ons are common. The league attends, films, and does not sing backup.
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: scoutcast.ai · sleeper.com · draftsharks.com