How do I stay calm with angry or rude users?

You have made peace with most users. It is the angry and the condescending ones who still slip past your guard and stay with you after the call ends. That is normal. Contempt and rage are designed to get under the skin. Remember what their tone is really about. The angry user is usually frightened and helpless in front of a machine they do not understand. The condescending one is often protecting a bruised ego. Almost none of it is about you. You are just the face that happened to be there when their frustration boiled over. When it lands, take one slow breath before you answer, and do not accept the invitation to fight. Solve the problem, stay level, and let their mood be their own. You are not required to absorb it or match it. Do the work well and let the rudeness pass through you instead of lodging in you.