Mind your manners!
Ever heard this one? “In English pubs, ale is ordered by pints and quarts. When customers got unruly, the bartender would yell 'Mind your pints and quarts, and settle down.' That's where we get the phrase 'mind your P's and Q's'”
Well, don’t be so sure. There are quite a number of theories about where the phrase came from, including a British play by Thomas Dekker that was all the rage in 1602, The Untrussing of the Humorous Poet in which a character, Afinius, says the immortal words:
“Troth, so thou'dst need; for now thou art in thy Pee and Kue: thou hast such a villanous broad back,” according to this website.