Effect:

After you and an audience both put your hands on the table, you twist your arm a full 360 degrees while he gets stuck halfway.

Preparation:

Long sleeve shirt.

Procedure:

1. Place your right hand on the table or sidewalk, with your fingers pointing towards your body. It should feel a little uncomfortable.
2. Your fingers should be pointing to the left now. Now distract him by saying things like "you're doing it wrong; do exactly what I'm doing!" or "Maybe you should back up a bit to get a better view of my directions."
3. With that, point to his hand or push him away a bit with your other hand, and start twisting your arm Counterclockwise while his eyes are concentrated on himself. Turn your palm up (while keeping the fingers pointing left) but keep turning the hand over the same way until it is face down again. With a long sleeve shirt, it looks as if your hand is just turned sideways to the left, but the truth is that it is twisted 270 degrees to the right.
4. After that, get him to do what you are doing again. Little does he know that you're simply Untwisting your arm instead of twisting it like him.
5. You can enhance the effect by placing a plastic cup under your armpit, it will make it sound like your bone is crunching. Remember not to show your arms, if not it would give away the secret to the trick.