I really confused the person monitoring the self checkout on one occasion several years ago.
I paid with cash, and was supposed to get something like $2.17 back in change. The machine gave me the seventeen cents just fine, but instead of two dollar bills, I got a one and a ten.
It took a couple tries to get the worker to understand that the machine gave me too much back.
I've had people try to slip me deals when an error occurs but I'm so genuinely in the moment I can't see it. Leads to awkward exchanges where they're trying to push free food on me and I'm just like "nah just a mistake bruh here ya go!"
And then facepalm 10 minutes later when the situation catches up.