What's the best way to respond to someone who insists on advancing an argument that appears to be completely insane? For example, someone like David Icke who insists the world is being run by evil lizard people? Or your friend the professor who thinks his latest "breakthrough" is going to make him the next Einstein but, when you ask him what it is, it turns out to be nothing but gibberish, meaningless equations, and surface analogies? (My father, the professor, has a friend, also a professor, who's quickly becoming a crank on the order of the TimeCubeGuy.) Or, say, this particular bit of incoherent political ranting?