Many years ago I had heard an interesting story. The "P's" and "Q's" in that particular pun stood for "Pints" and "Quarts". The story goes like this. Back in the old days in Ireland (I believe), the barkeeps would tell the patrons to mind their Pints and Quarts when they got really smashed and started fighting so they wouldn't break any more of the glasses. Later on the Pints and Quarts were shortened to P's and Q's. Not sure if it is true but it is a cool story all the same. Happy days and zippy renders!