Did you know…?
…that ‘minding your p’s and q’s’ dates back to a time when local taverns, pubs and bars served up their patrons drinks by the quart and the pint. Bar maids had to keep an eye on the customers and keep the drinks coming. They had to pay special attention to those drinking pints and quarts, p’s and q’s.
Today the idiom simply means being on the best behaviour, paying attention.