Thirty-Six Methods of Mathematical Proof (jwilson.coe.uga.edu)

Proof by profanity: (Bawdlerized geometry proof) "We have had it with these monkey fighting points on this Monday-Friday plane."

One more:

Proof by divinity: "Oh, for Christ’s sake!"

Proof by meditation/introspection.

I have done this following a lot of handwaving in an introduction to a chapter.