I work at a pharmacy/convenience store with discount cards. This just happened to me. It's about an hour before we close and some guy comes in and I say hello and he greets me back. In a minute or two he comes to the register with baby stuff (diapers and wipes I think).
I do my scripted:"Hi did you find everything ok? Do you have a discount card?"
He responded:"Yes I did an no I don't."
Me: "Alright then it'll be X dollars"
Him: "Why do you guys always ask that? I fucking hate it! Is there any way to get you to stop?"
Me: "Unfortunately no. That's our policy to ask for the card."
Him: "Well it's annoying, goodnight."
Me: "Alright goodnight."
Sorry man, didn't know having to answer a single yes or no question was so annoying.