From  u/FozzyOfH2 Tales From Retail:

Last year I got a job in a book/stationary shop in the UK, my first retail job. I'd heard stories of bad customers before and always thought if I had to deal with someone like that I'd be able to laugh about it and deal with it no problem. I underestimated how dumb people can really be.
I serve a lot of older customers in my shop, and a few of them do misread offers and promotions but it's always a minor issue. It was a major issue for this one guy though, who I will call CM (Confused Man). Our books in the book chart were on a buy one get one half price offer at the time. He brought a single book from the chart to the till.

Me: "Okay just the one book that's £7.99 please."

CM: "...£7.99 is half price?"

Me: "That's full price, however if you buy another book off the chart one of them will be half price."

CM: "But the sticker says buy one get one half price."

Me: "Yes, if you get two books, you get one of them half price."

CM: "No. No it says buy one get one half price. I am buying ONE, I get this ONE half price."

Me: "...Uh, no see if you purchase two books, the offer makes it so you're buying one book and getting the other half price. Buy one, get one half price."

CM: "That doesn't make any sense. I am BUYING ONE. I get this one HALF. PRICE. This is the one I am buying this is the one I get half price."

Me: "Okay let me put it this way, if the sticker said buy one get one free, you wouldn't get this one book for free right? You'd have to have two, buying one to get the other free. It's the same thing here but half price instead of free."

CM: "If it was buy one get one free this one would be free..."

Me: "..."

CM: "..."

Me: "It's £7.99 for the book."

CM: "Well I don't have that much money on me I only have enough for a half price book."

At that point he walked away from the till and out the door muttering something about "pathetic unhelpful staff". To this day I still wonder if that was the first time he'd ever encountered a BOGOHP offer before.

--u/FozzyOfH2