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Phrase(s): Who do you think you are?
Inf. Why do you think you can lord it over people that way?; Why are you so arrogant? (Usually in anger.) • Tom: Just a minute! Who do you think you are? You can’t talk to me that way! Bob: Says who? • "Who do you think you are, bursting in here like that?" sputtered the doorman as Fred bolted into the club lobby.
McGrawhill's American Idioms And Phrasal Verbs