Cashier Bad Custormer Service

My son was standing in the queue and waited to be served the cashier assisted other customers over him and when I approached him he shouted at me that he is waiting for my son to tell him what he wants,I then tild him its your duty as a cashier to ask the customer how can we help you,which is proper customer service and it is the umteenth occassion where he is confrontational with customers and he even started swearing at me. The cashier's name is Casper a Zimbabwean man working at Shell Vos Motors in Kraaifontein.