One of my favorites out of many:
After moving cross-country, I got a job as a manager at a chain bookstore. This was March. Right around that time, the company was running a brief promotion that sent out coupons for a free ereader if you bought their largest tablet model. Good deal, right?
Fast forward six months. In September, I had a customer approach me at the info desk and put down her tablet. She tells me she bought this in San Diego and then saw the coupon for the ereader when she got back and she wanted me to give it to her. She had a printout of the email advertising the deal but not even the actual coupon, and because the coupon is what shows the expiration dates, she kept claiming I had to give her this device. I stayed mostly polite throughout, explained repeatedly that this promotion was outdated, I wasn't going to honor it, yes I am the manager so no you can't talk to anyone else, and even if it weren't expired, you don't have the actual coupon code and without that I /still/ couldn't honor it. Finally she got super pissed at me and went to storm out. And me, snide bitch that I am, said very politely after her, "Have a nice day."
Lady turned around and proceeded to ream me out for the next couple minutes, none of which I heard because she decided to lead with, "You need to go to customer service school!" After she finally did stomp out, I spent the next several minutes sitting in the floor at info giggling to myself and asking my co-workers if they thought this school would be accredited and did they have scholarships because I work retail and I'm poor.