A very funny Do as I do-routine with 2 bottles and 2 tubes and an assisting spectator. The spectator follows every move you do but at the end his bottle is always upside down! The bottle is placed inside the tube and the tube is held between the hands and turned over a couple of times. When you raise your tube your bottle is always right side up, the spectator does the same but his bottle is always upside down!
As a final effect your bottle is turned automatically. Great comedy potential!