Years ago, through the wonders of the Rotten.com Library, I learned Godwin's Law of Nazi Analogies. Per Rotten.com:
Conversely, you can attack an opponent simply by declaring his position to be consistent with Hitler's. This tactic has long been a fixture of the Usenet newsgroups, which eventually prompted Godwin to formulate his famous Law of Nazi Analogies:
As an online discussion grows longer, the probability of a comparison involving Nazis or Hitler approaches one.
Whenever one of our