How to Perform a rigged impromptu matchbox game
This trick can be done anytime, anywhere, with one of the easiest props ever: a matchbox.
The props couldn't be simpler: just find an empty matchbox that has the same design on both sides. Set it on the table with the inside tray facing up (we'll call that "right side up") and start making a simple game of balancing the box with one side on the edge of the table and the other on your fingertip.
The challenge is to bring up your hand slowly enough that when the box reaches the vertical position, it stands erect without tipping over. It's okay if you flub the first couple of tries (it genuinely is a minor challenge), but eventually get it right and declare yourself "Awesome."
Once you've done it a few times, your mark should be interested in giving it a go himself. Explain the rules, and set it up the same way for him. First try, he'll probably get it (and not see what's so hard about it). Perfect. Once he has won a few times in a row, tell him he's only got beginners luck, and bet him a beer that he can't do it three times in a row.
Once he agrees, set up the box "right side up" for the first two tries, but for the third one, flip it with the internal tray upside-down. The box won't look any different, but this time, when he raises his fingers up, the distribution of weight inside the matchbox will make it impossible for him to win. Every time, the box will overcompensate and fall forward, guaranteeing you a free tasty beverage.