I work retail and have experienced it all. I genuinely enjoy helping people, but you're always going to have some jerk offs. It's especially compounding when you work in a technical/niche field that most people need but don't understand completely.
It's all about wording, examples, and analogies. Since I'm in management I also strive to get this from every employee. If I caught one of my guys doing anything I can't stand from other places, they're going to hear about it explicitly.