From Wikipedea about Goddwins law.
There are many corollaries to Godwin's law, some considered more canonical (by being adopted by Godwin himself)[3] than others.[1] For example, there is a tradition in many newsgroups and other Internet discussion forums that, when a Hitler comparison is made, the thread is finished and whoever made the comparison loses whatever debate is in progress.[8] This principle is itself frequently referred to as Godwin's law.[9]