Mind Your P's and Q's. What does this mean and what is it's nautical origin?
Damon and Dennis have some great explanation as to the origin of this expression.
Another is this. In the days of sail when sailors were paid a pittance, seamen drank their ale in taverns whose keepers were willing to extend credit until payday. Since many salts were illiterate, keepers kept a talley of pints and quarts consumed by each sailor on a chalkboard behind the bar. Next to each person's name a mark was made under "P" for pint or "Q" for quart whenever a seaman ordered another draught.
On payday, each seaman was liable for each mark next to his name so he was forced to "mind his Ps and Qs" or get into financial trouble. To ensure an accurate count by unscrupulous keepers, sailors had to keep their wits and remain somewhat sober. Sobriety usually ensured good behavior, hence the meaning of "mind your Ps and Qs".
It is really interesting to read all the different nautical explanations for the term "Mind your P's and Q's". There are probably more, so if you know another, please add below.