waffle tax
When you do someone the favor of bringing them food, such as waffles (reasons include too tired or too lazy to get one's own food) - it is OK to take a bite as a tax for the food delivery service.  Out of courtesy, the server will first ask - whether waffle tax is OK.
Kid: Mom?  Can you please bring me some waffles?

Dad: Get your own, you're old enough.

Mom: Sure, I can get you some.  Is waffle tax OK?

Kid: Sure, Mom.  Don't forget the syrup!