The thing with most fast food places (Mcdonalds etc.) the server isn't the one making the food, even when it is punched in properly by the cashier.
There may be stupid idiots in the kitchen that cannot make the burger properly, or don't read the grill slip so when the server gives the food to the customer. But if its not correctly made then it's the server/cashier that gets bitched at.
I had a lady one time who ordered a burger without lettuce. I went to get her burger and the grill slip said 'no lettuce' so I assumed no lettuce (as you cannot unwrap the packaging to look, and it was rather busy).
I handed her the burger, turned around to make a drink and when I turned back to the cashier the lady THREW the burger at me, it hit me, then screamed! "THIS. HAS! LETTUCE!" Then muttered about ME being an idiot... uugh.