I've got a better one -
Boy and his GF ordered 1 super burrito - Comes with rice, beans, cheese, sour cream and salsa ofcourse your choice of meat -
Dude ask for the burrito to be served open face in a bowl (we've been doing that for 11 years now), then proceed to ask if I can take the tortillas and the cheese and make him a quesadilla - I said sure, and rung him up for the quesadilla - He look stunned, ask me why I charged him for something that he was getting already. What a moe - I told his GF never to bring him with her again - She broke up with the idiot 2 weeks later.
Amazing, I have heard and seen as bad and worse though as restaurants. Such as bringing in your own drinks or sharing one cup with 2-3 people with refills or bringing in cup from last visit. Even worse stuff too but I am too lazy to post of these stories though. I have seen similar stuff at ranges too, people asking to go into indoor range as a spectator with a shooter and not to charge and then catching them shooting.
We used to have people get 8 or 10 water cups for their family. Then they all put Sprite in them. Sprite has bubbles, water doesn't. We used to just take the cups off the table when we pre-bussed, or just when walking by. We found though that it was just easier to not say anything, let the people think they got away with free sodas, that probably only cost us pennies. They would come back, spend 80 on pizzas next month, and steal $1 worth of soda.
I don't remember the actual food cost to us of a soda, but when you are buying it as a BIB, it doesn't cost much. Coke even made special deals with Quick Service Resturants like McDonalds to turn the syrup/water mix more watery. I don't remember the ratio, but McDonalds makes a killing on their sodas. Look at the price, $2 for 16oz, c'mon!? And, the syrup/water ratio is adjustable... I'm sure some business owners adjust the ratio... Just like some customers in the know, pop the cover and crank up the syrup. I'd get those rude awakenings Mondays while getting my morning coke. I don't drink coffee.