German expression. A person who does not allow any other opinion than his/hers; sometimes restricted to a specific area. A literal translation is "Opinion-Nazi".
Catherine: "Lost is the best TV serial ever"
Thomas: "Well, I don't like it that much."
Catherine: "I am seriously interested why you 'don't like it that much'. Explain!"
Steve: "Catherine, stop this shit you damn Meinungsnazi. Your ego does not allow that others have a different opinion about things you are crazy about. You always want an extensive analysis then!"