This is an idiom that at first, seems a bit strange, even to a native English speaker. Why Ps and Qs? What exactly does it mean?

Well, it means to “be careful” or “be respectful (i.e. to elders)” or simply it serves as a reminder to young ones to be polite and on their best behaviour in public.

Why Ps and Qs? It originally came from The English bartenders! “Mind your Ps and Qs” = mind (or tend to, watch out for) your Pints and Quarts…of alcohol! Don’t spill any!

Funny eh?

There you go. Another strange English idiom root uncovered.