Speaking of 'spitting' in nasty customer's food:

I used to manage a bar (15 yrs ago or so) and one night this very rude customer brought his drink back because it 'didn't have enough liquor in it.' The bartender put a little more vodka in it. A few seconds later the same guy came back with the same complaint (same drink). (Here's where he makes his fatal mistake) he actually turned his back to the bar! The bartender takes IT out and gives the drink a little stir and gives it back to the customer.

While I should have stopped the transaction, frankly there was too much opportunity for a classic story to stop it. I should note that I was also duly impressed with the tenders speed and agility in fixing the customers drink one handed.