I believe that you should listen to the person fully what he or she has to say, even if the person is screaming or shouting.... You have to be in control and be a good listener and observer. Once he/she has done with it.... if possible ask the person to relax and make them sit confortably. Your role starts now...Revisit what has been told and analyse the actual issue. Probably you may require a paradigm shift to fully understand the problem and come up with a resolution which is benificial for that person. There is no point yelling or shouting at an angry person. In other words, do not hit your head against the hard rock... stay cool :)