If a patron is very angry about something, pass them on to a supervisor.  It is not in our job description as circulation assistants to deal with that type of problem, and patrons often feel better when they get to talk to someone higher up.

If a supervisor is not available, try to remove the patron from a public area and make sure that #1 they know you are listening to them and #2 they know you plan to do something about it.  Fill out an incident report and forward it on to the appropriate individual so they can contact the patron to discuss the situation.