mind your p's and q's

mind (one's) p's and q's

To be polite and well behaved; to mind one's manners. Be sure to mind your p's and q's when you visit your aunt this weekend! The mother reminded her young children to mind their p's and q's when they went over to their friends' houses for play dates.
See also: and, mind
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

mind your p's and q's

or

watch your p's and q's

If you mind your p's and q's or watch your p's and q's, you try to speak and behave politely. She always minded her p's and q's in front of the queen, but their relationship wasn't that close. Note: This expression may originally have been a warning to children not to confuse p's and q's when learning the alphabet. Alternatively, `p's and q's' may stand for `pleases and thankyous', or expressions of politeness.
See also: and, mind
Collins COBUILD Idioms Dictionary, 3rd ed. © HarperCollins Publishers 2012

mind your ˌP’s and ˈQ’s

(informal) be careful how you behave; remember to be polite: Sally’s got very strict ideas about how her children should behave, so mind your P’s and Q’s.This expression probably refers to the P in ‘please’ and the pronunciation of ‘thank you’ which sounds like Q.
See also: and, mind
Farlex Partner Idioms Dictionary © Farlex 2017

mind one's p's and q's, to

To be very particular about one’s words and/or behavior. The original meaning of p and q has been lost, and there are various theories, ranging from “pints and quarts” in the bartender’s accounts, to children confusing the two letters in learning their alphabet, to the French dancing master’s pieds and queues, figures that must be accurately performed. The term was used from the seventeenth century on but is heard less often today.
See also: and, mind, to
The Dictionary of Clichés by Christine Ammer Copyright © 2013 by Christine Ammer

mind your p's and q's

Behave yourself. Opinion is divided over what the letters in the admonition to “mind your p's and q's” mean. They might have been two similar-looking letters that typesetters were warned not to confuse. They might have stood for pints and quarts that tavern keepers could have confused. Neither, however, is close to the idea of being on your best behavior, but p standing for “please” and q for “thank you” (pronounced thank-kew) does. And that's how generations of parents reminded their children to remember their manners.
See also: and, mind
Endangered Phrases by Steven D. Price Copyright © 2011 by Steven D. Price
See also:
References in periodicals archive ?
MIND YOUR P'S AND Q'S: London punk outfit Mouthwash playing The Parish
Mind your P's and Q's! Improving ARMA forecasts with RBC priors
The apostrophe (') serves three main purposes: to show that something belongs or pertains to someone (the boy's baseball, the man's red hair), to make a contraction (they're in a hurry), and, rarely, to form some plurals (mind your p's and q's).
Mind your p's and q's as well as your I's and t's and r's and a's.