Minding Your 'Ps AND Qs'?

HISTORY: 1700s-- At local taverns, pubs, and bars, people drank from pint and quart-sized containers. A bar maid's job was to keep an eye on the customers and keep the drinks coming. She had to pay close attention and remember who was drinking in 'pints' and who was drinking in 'quarts,' hence the term 'minding your'P's and Q's '
Photo by Fruits of Canning by upturnedface