I worked at a book store, and the card readers processed everything as credit. Which is generally fine, since most folks' debit cards can be run either way.

I had an old dude come up and pay with his debit card. When it didn't ask for a pin, he started screaming at me about how I'd just illegally charged his credit card. I politely explained that it didn't work that way and he just kept yelling. So I rudely explained that it didn't work that way.

Dude, you think you inserted your debit card and that magically, our system somehow found out your credit card information and charged that instead?

I played through a fair amount of Sniper Elite 2 before a friend saw some of my gameplay footage and was like "Damn dude, you don't even zoom your scope in?"

Turns out I'm just bad at reading instructions...