Saying "none of your business" can be considered blunt and potentially rude, especially if it's said in a harsh or confrontational tone. While it is a direct way of expressing your desire for privacy, it lacks the politeness and finesse that can help maintain positive social interactions. It's usually better to use one of the more polite approaches mentioned earlier to convey the same message while still being respectful and considerate of the other person's feelings. This can help prevent unnecessary conflicts or hurt feelings and maintain a more harmonious relationship.