I work self-checkout at a grocery store. Our store offers customers a coupon for 5% off their next purchase when they get enough "points" which you get by spending money with us. This is important.
A couple days ago an older guy came up to the self-checkout units and headed over to the one I was putting bags on (sidenote: there were 4 other open SCO registers he could have used, why do people do this?) and he told me to get out of the way. I had just finished anyway so whatever.
So I head back over to my area and he goes through his transaction, cursing and muttering at the register the whole time. He finally gets to the end, and a message pops up asking if he wants to redeem his points for a 5% coupon. He hits yes, so now a coupon will print out on his receipt that he can use for his next purchase. He stares at the screen for a few seconds, turns to me, and says "it said something about a five percent!"
Me: Oh, that comes out as a little barcode on your receipt and you can bring it in next time and use it as a coupon.
Old guy: You mean I can't use it now?!
Honestly the way the message comes up is a little ambiguous, so most of the time as long as people aren't being an ass I'll just put it in for them even though we're technically not supposed to. However, as this guy was being rude the whole time, I'm doing the bare minimum for him and going by the book.
Me: Yes, sorry. It's for your next purchase.
OG: But it said I could use it now so I hit yes!
Me: Well the machine's wrong
OG: Well that's stupid!
Me: Yeah I know, I'm sorry about that.
Around this time it started getting busy and all six SCO units were in use and I could hear the beeping from the alarms on my computer so I had to get back. He was kind of just staring at me not saying anything so I thought we were done and I walked back over to my area.
OG: Oh I see! Not your problem, right?!
Me: I'm sorry, I don't have any control over what the machines say.
At that point he turned back to his register and paid. As he was walking past me on his way out I told him to have a nice day and he told me to fuck off.