Anyone who has spent some time online, especially in forums or social media where chat and debate predominate, is likely to have come across references to Godwin’s Law, created by Mike Godwin in 1990:
As an online discussion grows longer, the probability of a comparison involving Nazis or Hitler approaches 1.
This builds upon reductio ad Hitlerum (aka argumentum ad Hitlerum or playing the Nazi/Hitler card), an association fallacy proposed by political philosopher Leo Strauss a few decades ago. Godwin says he aimed to:
build a counter-meme designed to make discussion participants see how they are acting as vectors to a particularly silly and offensive meme…and perhaps to curtail the glib Nazi comparisons. (Wired, 1994)
Godwin’s counter-meme spread successfully – so much so, that references to Godwin’s Law are now common enough for me to suggest reductio ad Godwinum as a recursive corollary:
As an online discussion of online discussion grows longer, the probability of a reference to Godwin’s Law approaches 1.
Have you ever invoked Godwin’s Law? And what other corollaries or fallacies might we idly invent?
Sentence first 
My CEO was recently compared to Hitler. It wasn’t particularly far into the Facebook conversation, however it did come after a long-standing community “grapevine” conversation outside of social media. Interesting post!
Thanks! Casual discussions can devolve remarkably quickly into grotesque hyperbole.