"Just a Q minding his Ps" is interesting. Dug into some meaning behind the idiom to see where it comes from, draw your own conclusions:

"To be very particular about one’s words and/or behavior. The original meaning of p and q has been lost, and there are various theories, ranging from “pints and quarts” in the bartender’s accounts, to children confusing the two letters in learning their alphabet, to the French dancing master’s pieds and queues, figures that must be accurately performed. The term was used from the seventeenth century on but is heard less often today."

Sauce: https://idioms.thefreedictionary.com/minds%20your%20ps%20and%20qs