My favorite to this day is from the Amazing Jonathan's "Every trick in the book" book. It is super simple and creates loads of laughs. Preparation is simple, go into your bathroom with a video camera, tape a shot of the toilet from as high as you can get the camera, tape about 5-8 minutes of this then put the tape into your VCR. Now you are set, all you need is a couple of unsuspecting visitors to come over. When they arrive one of them will eventually need to go to the bathroom, as soon as they go into the bathroom, let everyone else in on the joke and tell them to gather around the TV and to start laughing hysterically, then just when the person starts to come out of the bathroom hit play on the VCR. Now imagine yourself as the person coming out of the bathroom, you see everyone laughing and wonder "What's so funny?" then you see a camera shot of the bathroom on the TV, you of course assume they have been watching you the entire time through some sort of hidden camera ;) .
I have used my tape often and it is hilarious!