http://www.jargon.net/jargonfile/g/GodwinsLaw.html wrote:
Godwin's Law /prov./ [Usenet] "As a Usenet discussion grows longer, the probability of a comparison involving ***** or Hitler approaches one." There is a tradition in many groups that, once this occurs, that thread is over, and whoever mentioned the ***** has automatically lost whatever argument was in progress. Godwin's Law thus practically guarantees the existence of an upper bound on thread length in those groups.
I'd just like to thank the people who posted and defined this law for us.