TricksWithHats
Hold the arm out to the side and move the head so that you are looking directly along the arm.
Use the neck chop to knock the hat and a let it roll down the arm. Catch it with an inside grip.
Raise the arm up and flick the hat back along it. Tuck the chin in beside the shoulder as the hat gets close and it will pop back onto the head.
The key to this trick is to move your arm so that the hat is always rolling "downhill".