I worked in several restaurants While in High School and college as a line cook and pantry chef. I have never seen a coworker do anything disgusting to anyones food because they sent it back. Never, not even if the customer ordered a steak and sent it back because they thought it was cooked improperly, and it was cooked perfectly. You have no idea how many people order a steak rare but really want it cooked medium. I will always send food back if there is a problem with it, which is rarely. I send mixed drinks back to the bar all the time, so many bartenders don't know how to make a decent margarita, or bloody mary, etc. I always just get something else (Like beer) instead of having them remake the same terrible drink again.