This most commonly occurs with strangers, who don't expect to see you again and probably don't care about what you think of them. They don't bother to consider your feelings, especially if they're already emotionally bogged down by something else in their lives.Other times, you'll get into situations (e.g., at work or school) in which people are persistently rude to you. They may have some prejudice about your gender, race, occupation, etc. or may be judging you for something else that you've done. These people are usually obstinate in their views, however false they may be, and there is little point in trying to disprove their biases.