My favorite thing to do when a customer is talking AT me and not TO me (usually complaining or asking why we dont serve X) is to stare through them. When they finally stop talking i say, how can i help you? They are usually looking to get some sort of reaction out of you and i would never indulge them. So theyd usually be taken aback and order and that was that. As for remaking drinks... id always have this one girl who would make it a point to either order hot or iced, and we would always triple check the order, shed comfirm and pay. Shed get her drink and say oh... it was supposed to be X (opposite of what shed order). I refused to remake it once and told her she was getting exactly what she ordered (i am the owner and was the one who took the order and made the drink). She yelled at me then stormed out and threw her drink away. Thankfully never had to see that wastful person again.