Watch at this link for a fun back-and-forth between Jon Stewart and Bill O'Reilly on the argumentum ad Hitlerum.
TL;DR for O'Reilly, his Nazi invocation (about "the left") is just fine because his assistants found an anonymous commenter at a blog who called Nancy Reagan evil and wished that she die soon (of natural causes). What that has to do with the Nazis is beyond me.
That, of course, is some classic nut picking, or as the experts call it, weak manning. What makes it especially fallacious (if that is possible) is that it's deployed in an ideologically monochrome (should I drop this phrase? Should I not comment on my sentence during my sentence?) context in order to disqualify an opposing arguer on account of the very bad arguments they make. This last part being critical to the nutpicker.