When parents ask that rhetorical question, they are trying to prompt their child to say "thank you." What do you do if your child slyly answers, "Now!" You could try a little bibliotherapy by reading them Perfect Pigs, an Introduction to Manners by Marc Brown and Stephen Krensky. Search for 'children and etiquette' in the library catalog and that book and many other gentle approaches to teaching manners will turn up, like Hello Gnu, how do you do?: a beginning guide to positively polite behavior by Barbara Shook Hazen or It's a spoon, not a shovel by Caralyn Buehner. Not everyone's parents have done their homework though judging by the incidents of road rage and other rude behaviour that we all experience everyday.
What do you do when you encounter someone who as a child has not absorbed those gently humorous nudges to say please and thank you and is now tailgaiting you on Route 78, or taking the parking place you have been waiting for, or drinking the last cup of coffee at work and never ever starting a new pot? These daily examples of rudeness and how to respond to them constructively are discussed in P.M. Forni's The Civility Solution, what to do when people are rude. Professor Forni teaches Italian literature at Johns Hopkins University and founded the Civility Initiative in 2000. His book Choosing Civility was a bestseller and the Civility Solution continues the good fight by suggesting very practical ideas for people who want to know how to not only be more polite, but also to encourage politeness in others.
For an interview with P.M. Forni read this article in the Johns Hopkins Gazette.