J. Douglas G. answered 12/25/20
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"Ich verstehe nur Bahnhof" essentially means "I don't have a clue." Bahnhof is the German word for train station. For people only passing through, not needing any real understanding of the language, finding their way back to the train station was all they needed. The idiom locked in as an indicator of someone with no knowledge and no interest in developing any, but usually in the third person, e.g. er versteht nur Bahnhof -- he doesn't have a clue. And yes, it IS a micro aggression!