I've never gotten my order screwed around in a
real restaurant, but if it were, then I'd just alert the waiters calmly. Fast food restaurants are a different story altogether; I can understand that there's a lot of pressure involved in maintaining order and getting said order right (

). But it still really irks me when they get my order wrong, even if it's something really simple. The main offender is McDonalds, which I hardly ever go to anymore. I guess there's something about the heinous atmosphere at McDonalds which makes me all testy. (Speaking of testy, y'know what they put in their foods..?)
It's just habitual now for me to thoroughly check my (take-away) order whenever I receive it at any fast-food place. I'd say about every two times out of five the order will be incorrect. And I'm pretty sure it's like a 1/8 success-rate in the drive-in queue.
Jam it back in, in the dark.