That Logic Doesn’t Pump

I work at a gas station where the pumps are all prepay only, but we can override it and turn it on if someone leaves a payment method in the store beforehand. A guy came in today and gave me $60.

Customer: “Don’t charge me out with the cash.”

I thought that was weird, but whatever, I flipped it on anyway. The guy filled up and then came back in.

Customer: “I’m going to pay with card.”

Me: “Okay, cool.”

I gave him the money back and rang it up.

Customer: “Wait, that total isn’t right. You didn’t give me the cash discount.”

Me: “You’re not getting the discount because you’re paying with a card.”

He looks at me like I’m the stupid one and starts waving the cash around.

Customer: “But I have it right here!”

Me: “That’s not how that works. If you want the cash discount, you have to pay using the cash.”

Customer: “You didn’t specify that!”

Me: “I didn’t specify that to get a cash discount, you have to pay using cash?”

Customer: “Yeah!”

Me: “Well, that doesn’t change the fact that I can’t give you the cash discount unless you give me the cash.”

Customer: “I’m never coming here again!”

Me: “That… is acceptable.”