Godwin's Wall

The point in a conversation at which you realize that the person you're talking to is an intractable Nazi (or close enough). Usually encountered during "alternative fact"-laden discussions with supporters of reactionary movements, e.g., Donald J. Trump.

When Mr. Bannon started frothing at the mouth and calling me a "Cultural Marxist", we sorta hit Godwin's Wall, so I sent Mexico the bill and left.