I own the [Yogurt Store] that I also work at as a cashier so I don't have to pay somebody else to do it.
I'm working the register and I'm one of the two people there. My other guy is inside the preparation area. A weird-looking customer comes in the store and grabs a cup without asking for a sample cup (this isn't normal behavior for a regular customer)
He fills up to the brim and beyond and comes to the register. I'll be 'Me' and he'll be 'WC'
Me: Hello, how's your day?
WC: Ring this up for me, chief.
Me (inwardly): Ruh-roh, he's one of those guys.
Me (outwardly): Okay, this is $27. Are you a [Rewards Program] memeber?
WC: I shore am! And I'd like to use my birthday treat.
Me: Okay, can you scan your card/phone please?
WC: That's not necessary, you can get the info from my credit card.
He hands me his credit card and waits for it to work. The birthday treat is some free yogurt.
Me: Sir, I can't use your birthday treat unless you give me your card.
WC: Fine-uh, here it is.
Me: I'm sorry sir, but it says you haven't earned a birthday treat yet.
WC: Well, my birthday is tomorrow, so can you just give it to me now?
The system doesn't work like that, and after a few minutes of me explaining that I can't do it, he says
WC: Well if you can't do it, get me a manager.
Me: I'll grab you a manager.
I promptly go into the back and talk with my employee and and make it sound like I'm asking him to go out with me. I change my shirt, go out alone and put on my biggest smile.
Me: Hello, I heard you asked for a manager. What seems to be the problem?
WC (looking at his phone): Your stupid employee couldn't give me my birthday discount.
Me: When is your birthday, sir?
WC: It's tomorrow and I want to get my treat today.
Me: I'm sorry, but we can't do it until tomorrow.
WC: Seriously? [He looks up right then] Wait, I ASKED FOR A MANAGER! GET YOUR STUPID (face) BACK IN THERE AND GET A MANAGER!
Me: I am a manager. I also happen to own this store.
WC: Your system is SOOOO stupid, I'm never going to come here again!
The weird customer walked out without his yogurt. He came back the next week and tried to use his birthday coupon again, but he had already used it at another store.