mind one's ps and qs
Unknown. Suggestions include an alteration of "mind your 'pleases and 'thank yous"; the phrase meaning "be mindful of how many pints and quarts you are drinking because it is starting to show in your behavior"; or in typesetting where letters are set in mirror orientation and a lowercase p and q can be easily confused. Early usage of "be on one's ps and qs" ("in thy Pee and Kue" in 1602) might refer to a sailor's pea-coat and queue (tarred pig-tail).
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