idiom

- to make an effort to be especially polite in a particular situation

(Cambridge Advanced Learner's Dictionary)

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The expression "mind your p's and q's" has been around for several centuries. One of the earliest written records was in the early 17th century. Etymologists have been arguing nearly as long about its origin.

Some of the theories are what we now call "urban myths," but they are fun to consider anyway. Here are the top four:

(1) Children learning to write were always reminded by their teachers to be careful not to reverse lowercase p's and q's

(2) In the days when type was set by hand, printers could easily mistake lowercase p's and q's

(3) The habit of adults wagging their fingers at misbehaving children often meant they were being reminded to say "please" (p) and "thank you" (when spoken together the "k" and the word "you" sounds like someone is pronouncing the letter "q").

(4) Pubs used to keep a record of the pints and quarts drunk by patrons on a chalkboard. Drinkers were thus encouraged to keep an eye on their p's and q's to prevent the barmaid or pub owner from artificially inflating the count.

Although nr (4) is the most frequently-cited origin, during the time the expression developed, pint and quart measures didn't exist.

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SMUGGLE OWAD into today's conversation
Say something like:

"We always need to mind our p's and q's, especially when dealing with colleagues from other countries."