The loser choreographs and performs a solo 'flash mob' about their fantasy season in three separate public locations, committing fully each time as though backup dancers exist. They do not. Music plays from a bluetooth speaker they must also carry.
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: fantasypunishments.com