Climbing.

For any of you who have ever even tried rock climbing or losing weight to do better in a competition:

http://www.rockclimbing.com/Articles/Training_and_Technique/What_Not_to_Do_at_a_Comp__265.html

Don't wait until the day before/of to optimize your power to weight ratio. Though I do have an appreciation for the skinny girls that excuse themselves from a dinner-date to go purge. As long as they carry breath mints with them, anyways.