From a math textbook I was reading recently — the legendary philosopher in action:

[A] proof containing a single error in reasoning cannot be considered “nearly correct”; we can derive any conclusion from a single false statement. Bertrand Russell (1872-1970) once stated this in a public lecture and was challenged to start with the assumption that 1=2 and prove that he was God. He replied, “Consider the set {Russell, God}. If 1=2, then the elements of the set are one element, and therefore Russell=God.”

That may be apocryphal, but if true, it’s a hell of a line to come up with off the top of your head.

Update 7/5: In comments, Michael Koplow directs us to a demonstration of the same principle in Zero: The Biography of a Dangerous Idea. The author, Charles Seife, intentionally divides by zero to show that it allows him to prove that Winston Churchill is a carrot. Here’s the Amazon Search Inside the Book link so you can read it for yourself.