Have you ever had someone scold you about pointing at something? Have you ever had someone interrupt you to tell you that pointing is rude?
I don't know about you, but when I was growing up, pointing wasn't emphasized as something rude (in fact, everyone did it, even people who complained about it being rude) but interrupting was very rude (but the complainers still did it). So who determines what's rude?
Consider slapping. In my book, slapping someone is very rude, but I've been told that some places in Europe slapping is a form of greeting. Belching. That seems pretty rude but in some cultures it's actually a complement to the cook to let out a good, healthy belch at the end of the meal.
The reality is that rudeness doesn't have an ultimate standard. It's not an issue of morality which is defined biblically. Sure, God gives us a moral standard, but he doesn't give us a rudeness standard. If defending against rudeness violates God's morality, it is obviously immoral!
I recently heard about a father who thought that elbows on the table was rude. He stabbed his children with a fork whenever he caught them with their elbows on the table! Sure, he taught his children that elbows on the table was rude, but at what cost?
We all need to learn to have a Philippians 2:3 kind of attitude - "Do nothing from selfishness or empty conceit, but with humility of mind regard one another as more important than yourselves." (See also Romans 12:10, 16; Ephesians 4:2, 32.) We need to see others' actions from their point of view rather than trying to force them to accept our point of view. Are we really right and they are wrong? Instead, unless they clearly violate God's moral standard, let's be humble about the situation. (Even as parents, we need to practice humility. When Peter quoted "God opposes the proud" (1 Peter 5:5), he had just specifically addressed the elders and young men, but he was talking to the whole church.)
If someone is "rude" around you, first, take it to God and ask him if he wants you to deal with it or let it go. If he wants you to confront the rudeness, do it with compassion. Don't exasperate your children (Ephesians 6:4), or others for that matter! Sarcasm, insults and violence have no place in loving correction.