Why are friends rude sometimes?

It is impossible to read the minds of other people. If a person is blatantly ignorant or hateful, that is one thing. But subtle social slights or confusing rudeness is frustrating, and ultimately the best thing to do is to not take it personally. Make a mental note of what happened, and if you notice a pattern, it might show what causes that person to be rude. It also could help you to realize they are not a good friend. In general, though, people being rude is sometimes unavoidable and usually not worth worrying about. Instead, try to be a kind, direct, and conscientious person, so that you can rest assured that your behavior is not rude or prompting particular rudeness in others.