TricksWithHats
Use a palm-up fork grip at the back of the hat and remove it, straightening the arm. As the arm straightens twist the wrist and take the ring finger off the brim. Spin the hat so that it moves between the middle and forefingers, then transfer the grip to the forefinger and thumb and continue the spin for as far as you can.
Reverse the "twiddle" to place it back on the head.
The main video clip for this trick doesn't show the fingers in any great detail. See the closeup version (120K mpeg) for a better view. For best results you might want to set your video player to loop the clip.