As an online discussion grows longer, the probability of the statement 'foo' occurring, halting useful discussion, approaches one, where 'foo' is some MemeticAphorism.  

FoosLaw was inspired by, and is a generalization of, GodwinsLaw.

Some special cases:
* foo == "a comparison involving Nazis or Hitler": GodwinsLaw
* foo == "a reference to 9/11" (NineEleven) : GodwinsSecondLaw
* foo == "GodwinsLaw" (related to Miller's Paradox, Quirk's Exception; see below)
* foo == "commie" or "communism"
* foo == "terrorism" or "Osama bin Laden": related to GodwinsSecondLaw

I couldn't put this in the same list:
* foo == "YouArentGonnaNeedIt"

First articulated by TimLesher.
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These used to appear in the wikipedia article on Godwin's Law but were purged:

Quirk's exception: Intentional invocation of this so-called "Nazi Clause" is ineffectual.

Miller's paradox: As a network evolves, the number of Nazi comparisons not forestalled by citation to Godwin's law converges to zero.
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See
GodwinsLaw,
QuotingNotThinking,
LaynesLaw.