Those who cannot tell the difference between rudeness and lack of manners will never be rude, and will always lack manners. A rude person is, by definition, an intelligent person, a fast thinker whose words can be as sharp and accurate as a surgical obsidian blade. Good manners, on the other hand, are a matter of education - we learn them rationally, and by reason we can keep them or not. Without reason and education, we are reduced to savages with little more than sticks and stones.
But then again, there's quite a lot of people out there who seems to have come down from the trees, but barely.