Godwin's law
From Cfcot
Godwin's law of Nazi analogies states that as a thread gets longer the likelihood of a Nazi or Hitler analogy being made is equal to one, i.e. certainty. By mentioning Nazis or Hitler in a thread that has nothing to do with these topics, one is assumed to have forfeited the debate.
It is often invoked on the Off-topic boards. Not to be confused with the user Godwynn.
