Godwin's Law was introduced into electronic discourse around 1990, & referred to discussions on Usenet (that was back in the internet's pre-www, pre-GUI Olden Days, sonny).
The law states: "As a Usenet discussion grows longer, the probability of one side likening the other to Nazis or Hitler approaches 1."
And my favorite corollary is "The first one to mention Nazis or Hitler loses the argument."
Swobbie
who used to chip out her computer programs onto stone tablets
ps. Also see Reductio ad Hitlerum