in my second year of high school i got a job a burger king (or Hungry Jacks, as it is called in the state of Queensland, Australia) and if a customer pissed me off i would vent the anger by writing a message in the burger with the tomato sause, it was just a bit of self gradifacation. i would never spit in someones burger, thats just gross, but this was my way of getting back, without getting cought.