A variant of Godwin's Law: As an online discussion of gun owners' rights grows longer, the probability of an ad hominem attack involving penis size approaches 1.
Person 1: I carry a gun to try to keep my family and I safe by exercising a Constitutionally-protected natural right.
Person 2: Hah! You carry a gun because you have a small penis, and you are trying to make up for it!
Person 1: Well, I guess Markley's Law is still true.