The Bet:
Place your hat over a shot. Tell you victim that you can drink that shot without touching the hat.

The First Solution:
Stick your head under the table or bar and make drinking noises (Gulp?). Come up and say you've done it. When the sucker says, you didn't drink it say "Sure I did, check for yourself". When he lifts up the hat take your drink.

The Second Solution:
Tell the sucker you feel bad about taking his money so easily and tell him you'll let him try. When he goes under the table, pick up the hat, drink the shot, and put the hat back. When he comes back up, play along and lift up the hat and pretend to be just as surprised as he is.