It's can't be done" you exclaim. This is sure to get your marks attention. "There is no way it can be done." after saying this a few times the question of what the heck you are talking about is sure to come up. You can't pick up a shot of whiskey without spilling a drop. Your mark is sure to think he can, and the challenge starts. The whiskey is poured, and you go over the rules. You can't spill a drop, I won't push you or anything like that. They will of course say okay. Well why don't you put your money where your mouth is, a bet is made. Who could say no, it sounds so easy.
Pull out a laminated card ( a credit card should do) and place it on top of the glass. Place the glass and card on the table. Pull away the card, and there is no way the mark can win. The whiskey is touching the table, any movement will make it spill.