Godwin's Law

From Dar

Godwin's Law is one of the earliest documented indications of internet culture self-consciousness developing its own folklore.

From wikipedia:

Godwin's Law is an adage in Internet culture that was originated by Mike Godwin in 1990. The law states that:

As an online discussion grows longer, the probability of a comparison involving Nazis or Hitler approaches 1.

Although the law does not specifically mention it, there is a tradition in many Usenet newsgroups that once such a comparison is made, the thread is over, and whoever mentioned the Nazis has automatically lost whatever argument was in progress.