If you have spent more than 3 minutes in the hospitality business there is undoubtably some people who will really piss you off. How you maintain your composure, and your smile, and still make those people who piss you off want to come back and give you and your establishment some money is a small part of what makes you a good bartender. On the other hand, most of us would like to do something like this to more than one of our regulars.
Mentos Ice Cubes
Problem Imbiber 