The loser spends one full night sleeping outside, backyard tent or balcony, on a date the league chooses, which is always in winter. Screenshots of the overnight forecast get pinned in the group chat. Hot cocoa is permitted; going inside is not.
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: fantasyfootballunlimited.com