Hitler would have been greatly offended if you called him a Nazi. Though embraced by extreme alt-righters today, the fascists of WWII Germany generally avoided the term, which was a colloquialism for "dunce" in southern Germany before the war. The word got applied to them when fleeing anti-fascist Germans cleverly abbreviated Nationalsozialist, an already shortened version of the party name. This spread to the countries they migrated to as a general term to encompass Hitler's group (who would've preferred NSDAP). The pejorative colloquialism Nazi was a nickname for Ignatz, a common name much like "John", with a country-bumpkin connotation of stupidity and ignorance. This in turn likely derives from Latin Ignatius, a Biblical name with possible origins in Ancient Greek, or Latin, or something. Honestly, etymologists aren't completely sure. But we are positive about the whole Nazi-insult thing. Believe me.
Adam Aleksic, a freshman studying linguistics at Harvard University, has been described as the internet's sixth most famous etymologist. He has disturbing interests in words, vexillology, geography, board games, limericks, and law, and he loves writing about himself in the third person.
The Etymology Nerd