Answer:
unreasonable demands
Explanation:
This specific customer is making contradictory demands since he/she first complains that the breakfast is too cold and then that it is too hot.
The problem here is not the fault of the waiter or the kitchen, the customer is probably frustrated about something else (or has some type of internal conflict) and just decides to be rude or irrational with his/her meal. No matter what service is provided to the customer, he/she will complain about it just for the sake of complaining. This type of customer is classified as chronic complainer.