This is a very difficult discussion that I frequently have to have with my employees and peers. While no one wants to hear this type of feed back, it is a great chance for someone to fix a problem they do not even know they have. First, make sure that the conversation is private and ask the person if it is a good time for some feedback. Using specific examples will help because saying always and never will only make you seem emotional. Describe the situation in which the person was rude, the ramifications and then ask them what they could have said/done differently. When people feel they have come up with the solution, it much easier to keep their buy in to improving.