Your hired help is worthless.
"Can I get fat fries with that, please?"
"We don't have fat fries."
"But the menu says…"
Okay, never mind. Just the regular freakin' fries and maybe a drink.
Charge a high price for drinks to go with the meal, but don't bother making sure the drink dispenser actually works.
So, what do you do when your customers report that there's something wrong with the drink dispenser? Say, "Oh, we know… Have some lemonade instead."
Way to try, there, Fatburger. We'll be spending money elsewhere.