If you work at a restaurant, you should know that writing something offensive on your customers' receipt is a bad idea. You have about a 0% chance of getting away with it and will inevitably be fired once you are caught. It only takes a few hours for pictures of the receipt to go viral online. The following video is about a restaurant worker who did not take this advice, and proceeded to write something terrible on a customer receipt. Shockingly, she noticed it.
The employee responsible seems to be the restaurant owner's son, and is still currently employed. We'll see how long that lasts.