From my friend Matt, this is pretty hilarious:

Godwin’s Law (also Godwin’s Rule of Nazi Analogies) is a mainstay of Internet culture, an adage formulated by Mike Godwin in 1990. It is particularly concerned with logical fallacies such as reductio ad Hitlerum, wherein an idea is unduly dismissed or rejected on grounds of being associated with persons generally considered “evil”.

The law states:

“As online discussion grows longer, the probability of a comparison involving Nazis or Hitler approaches one.”