I haven't yet had the opportunity to try this one, though it happened to a friend's brother.
There's this stuff called Ambusol (sp?). It's topical novacaine gel. Anyway, you dip someone's toothbrush in it. It dries clear and has not taste or smell. So the unsuspecting victim puts some toothpaste on, then brushes their teeth. The ambusol kicks in, and their entire mouth (assuming they brushed well) goes numb. Not only that, but they start drooling. So they have a numb, drooling mouth for quite a while. I think it takes a few hours for that stuff to wear off completely.
