I made a waitress cry once. I said something slightly sarcastic which wasn't directly at her at all and she 100% deserved it for being rude to me first. I'm assuming she was already having a bad day or something happened before that and not really my fault. BUT... regardless if it was her fault I had the power advantage and it hit me hard and I felt like a complete asshole and it made a lifetime impression on me. That was 25+ years ago and ever since I make it a point to be polite and generous too all wait-staff/service-people and every single time.

Well that was a little off topic and not what I was originally going to write but I'll leave it.