That's not an attempt to lessen the challenge they present as they can certainly make a waiter or manager's shift memorably miserable.
Many times there are reasons that the customer is responding in such extremes.
5.Make an extra effort to help them solve their situation. Even if the words are right, demeanor, tone, eye contact and body language can shout at a customer that they are a problem. Be aware of your physical posture, positioning of your arms and hands, plus your facial expressions as all these can cancel out what you are saying. 2.Look at the person who is talking to you as that validates you are paying attention. 3.Take notes as needed.