Chef's kiss

When a rude or objectionable customer sends their plate of food back to the kitchen with an insult to the chef and/or kitchen staff whilst being rude to the waiter or waitress, and in response the chef Hawks up phlegm or even worse before it is returned to the customer. And I think that is the worst chefs kiss

The chef was angry and so insulted by the complaining customer that they returned the plate of food with a nasty chef's kiss to the unsuspecting customer