know (one's) shit(redirected from one knows one's shit)
know (one's) shit
rude slang To be very knowledgeable, especially in a particular area. That piano tuner really knows his shit—you won't believe how good the ol' Steinway sounds now. A: "I don't know about running this play, it seems like the wrong move." B: "Don't worry, Coach knows his shit."
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