A person in the National Socialist German Workers' Party or supports it. Mostly hate Jews (mostly Hitler) and support the so called "Aryan" race. This party ran Germany all the way from 1933-1945 it ended when Germany was defeated by the USSR, or the Soviet Union.
The Majority of Germany in WW2 were Nazi Supporters.
A common twitter insult used against people with opinions opposing those of leftists. It is used to bully people into abandoning their current stance or used to cancel someone, often unfairly.
"How dare you disagree that biological sex is immutable, you're a Nazi"