The first thing was probably a set of earrings when I was a really little guy. I handed them to my mom when we got home and she was shocked at what a smooth swipe I pulled and we immediately went back to return them. So much for my thoughtful gift! Hahaha.
I also recall this thing at my very conserva-religious elementary school, where people set up a little market selling things as gifts and such. I was given some money to go buy presents for people, but nobody told me how to pay for anything, and I assumed it was like a big box store where you pay at the end.
So here I am like, what, 6 or 7 maybe? Going from table to table and just yoinking knick-knacks into my little bag. Nobody stopped me or otherwise corrected me. I still don't see anywhere to "check out"! I end up just leaving, basically.
Cut to me waiting in the lunch line and just getting straight up shaken down and accosted for cash by some authoritarian staff types. I just handed them the bag of spending money I'd been supplied with and I don't really remember what happened after that. Looking back though, those people were very mean to a confused child under 10, treating me like some deliberate criminal mastermind of petty-thievery lol.