I waited tables for three years, made/delivered pizzas for about five, and did a little kitchen work too. Most of my friends worked extensively in restaurants - one is a professional chef.
In all that time and experience, I have never seen anybody do anything to a customer's food, no matter how obnoxious they were. My friends all said (I asked, for a column I wrote) that they never did either. They all had stories like TLTS's, but all were "I heard from someone who heard from someone" variety.