Secret: 1. Both of you take a drink. 2. Hold your drink forward in a toast. He does the same. 3. You take a drink. So does he. 4. You toast again. He does, too. 5. You spit a mouthful of your drink back into your glass. He can't--he's already swallowed!
Now, remember: the more you dress up the presentation with red herrings, the greater the chances they'll miss your mouthful of drink. That's why we start with the mirror setup... fussing over all the props on the table. Notice also the bizarre rituals as part of "the mirror" (by the way, for those of you wondering... yes, that's a reference to "Mr. Show" in there). But most importantly, notice that after the first drink, I make them say something... that reinforces the point that we've both swallowed our drinks. That way, second time you start the ritual, your sucker expects that he's about to say something, guaranteeing he swallows first (and buys you a drink).