Step 1 Record an empty bathroom for about 5 minutes.
Step 2 During the process of recording your bathroom, stage a fake wave in front of the camera using a friend.E
Step 3 Edit your video and burn it to disc
Step 4 Finally, the next time somebody leaves the room to use the bathroom..Put the disc in your dvd player and hit play. When they come back react as if you just watched them using the bathroom and watch them freak out.
I made this into a video: