It says... "I give god 10%, why do you get 18%?"
In the comments on the post, the person who submitted the image explains that this was just a portion of the total bill for a table of 20, which means the 18% tip is automatically put on the bill.
“Parties up to eight at my work may tip whatever they’d like,” explains the server, “but larger parties receive an automatic gratuity. It’s in the computer, it’s not something I do.” The auto-gratuity policy is apparently also listed on the menu.
In total, the group ran up more than $200 worth of food before tax and tip, says the server. As for whether or not the zero-dollar tip reflect the quality of service, the waiter writes, “They had no problem with my service, and told me I was great. They just didn’t want to pay when the time came.”