Grab a jug with a handle, fill it 3 quarters of the way full, and hold it in one hand fully extended skyward, and shkake it vigorously.
BETCHYA CAN'T KEEP YER HAND IN ONE SPOT WHILE THE WATER SLOSHES ABOUT...
First one to show video evidence of accomplishing such a feat gains ultimate bragging rights for exactly 5 minutes, or until I find something else to do in my state of boredom.