I'm told "We don't have one of those." Or I'm charged separately for two burgers, a drink, and fries. Or I'm given two cheese burgers instead.
I ask for the Two Cheeseburger Meal with no cheese and I'm told sure, no problem but then I'm STILL given two cheese burgers. Or they give me hamburgers in cheese burger wrappers. (Which isn't nearly as bad as getting a burger I can't eat, but still WTF)
Honestly, these people can't be stupid, but how hard is it to leave out the cheese?