As someone who worked as a cashier in a supermarket, I can't express how annoying is to deal with those customers that think they are VIP privileged!

Rule of Retail 1: There will always be an upset child. If there is not an upset child, there will be an adult ACTING like an upset child.
Rule of Retail 8: The customer is always right is a service attitude and not to be taken literally. The customers who do take it literally fall under Rule 1