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Phrase(s): You’re the doctor.
Inf. Fig. You are in a position to tell me what to do.; I yield to you and your knowledge of this matter. (Usually jocular; the person being addressed is most likely not a physician.) • Bill: Eat your dinner, then you’ll feel more like playing ball. Get some energy! Tom: Okay, you’re the doctor. • Teacher: You’d better study the first two chapters more thoroughly. Bob: You’re the doctor.
McGrawhill's American Idioms And Phrasal Verbs