2 ideas:
The Anime Marathon.
You must watch every episode of Dragonball, Dragonball Z, and Dragonball GT without sleeping. 5 minute bathroom breaks are allowed and food and coffee are provided to maintain energy.
Or
The Anime Iron Man competition.
8 hours of cute anime (CCS, Bottle Fairy, Azumanga Daioh, etc.), 8 hours of hardcore action anime (Fist of the North Star, Dragonball Z, etc.), and 8 hours of weird anime (FLCL, End of Eva, Death/Rebirth, Paranoia Agent, etc.)
Last one to go insane wins.