I'm guilty of the same thing, kinda.
when i was 15, working at the Akron, OH, mcdonalds location in the 44305 zipcode...
I would sometimes give my brother some extra fries when he came in and ordered a meal. Like, he'd order a medium Fry and he'd almost get a Large amount.
That was summer of 1992. I'm sure the statute of limitations has run out, so I'm okay with admitting this now.