mind p's and q's
mind (one's) p's and q's
To be polite and display good manners. Be sure to mind your p's and q's when you visit your aunt this weekend! The mother reminded her young children to mind their p's and q's when they went over to their friends' houses for play dates.
mind one's p's and q's.
Prov. to behave properly; to display good manners. When you children go to visit Aunt Muriel, you'll have to mind your p's and q's; not like at home, where I let you do as you please. We'd better mind our p's and q's for this new teacher; I hear he's very strict.