Put on a pair of butterfly clamps (They have other names, the ones that pinch harder when pulled on). Tie a bootlace to the chain between them at a point where the other end hangs down as far as your knees, then tie the other to a full 2L pop bottle. (If you don't have a full one, you can fill an empty one with water rather than waiting until you can buy one). You may not bend your knees at all. Pick up the bottle in both hands and stand upright, feet shoulder width apart, and hold out your arms shoulder height, fully extended, and then drop the bottle. Repeat 15 times or until you can't stand it any longer, but if you quit early, you may not touch your nipples until your next challenge.