Not the law about poetry formulated by American poet Edgar Allan Poe; that law was about the proper length of a poem ("The unit of poetry must be fixed by the reader's capacity of attention, and . . . the limits of a poem must accord with the limits of a single movement of intellectual apprehension and emotional exaltation"), but the law about parody and religion discussion on the Internet. The initial formulation by Nathan Poe took place in a discussion thread on August 11, 2005 at Christian Forums.Com. You'll note that the first version refers only to Creationism, but that the final, and most cited version refers to fundamentalism in the sense of all versions of religious fundamentalism:

Without a winking smiley or other blatant display of humour, it is impossible to create a parody of fundamentalism that someone won't mistake for the real thing

There is of course an inverse corollary which states that that non-fundamentalists (of whatever stripe) will often mistake sincere expressions of fundamentalist beliefs for parody.

Both of these expressions are clearly demonstrated on a daily basis on any number of Web pages and Internet sites. But, it is the nature of both Poe's law and its inverse that I don't even dare post examples, because someone, at either end of the spectrum, will not realize that the site is a parody—and madness will ensue, and sooner or later someone will invoke Godwin's Law.