A fork of Rural Dictionary
Spec. used by troublemakers and geezers
1. adj. to be on your best behaviour (Please and Thank Yous)
2. adj. to be drinking and smoking (weed) heavily (Pints and Quarter -Ounce of weed-)
1. "Police are watchin me tonight mate, I best be on my Ps & Qs."
2. "Grab us that corner booth in the pub so we can get down to our Ps & Qs."
Mind your Ps and Qs means to watch your manners, or be careful how you behave. It comes from Please and Thank you.
Your great-aunt's coming to tea and she's really fussy about behaviour - better mind your Ps and Qs.