Effect: Bet your friend that you can drink 2 pints of beer before he can drink two shots of his favorite liquor.
There are only a couple of rules: each of you can use only one hand (no double-fisting), nobody can touch each other (no wrestling), and nobody can touch each other's drink glasses (fair enough). Oh, and all you need is just a little head start: he can't begin his shots until after you've finished your first drink and set the glass on the table. Totally fair, right? Even with the head start, that's still 2 little shots against a whole second pint of beer!
Secret: Line up all 4 drinks, and start on your first one. As you drink your pint, your friend will wait and watch anxiously. He'll have his fingers poised to grab the first of his shots. Just before you finish your first pint, remind him that he can't start until you set your glass on the table, and that nobody can touch each other's drink glasses... Then with a grin, turn your empty pint glass upside down, and set it on the table over his other shot glass. Now he's stuck! He can't touch your glass, and thus can't finish his second shot!