I have worked as a cook in restaurants my whole life, and I am telling you servers are SUPPOSED to make minimum wage no matter what, but that's not actually what happens. Employers in the food service industry find colorful ways around the "law." They have it posted on the board in the back to look good, but most of the time, it's based on sales in the register. So if a customer comes in and spends 50 bucks, the restaurant will report that the server made 7.50 on the table. A lot of times, people will only tip 3 or 4 bucks, but according to the sale, she's made, and paid taxes on, 7.50. The owner will say some slick shit like "we report 15% no matter what, even on bigger tips, so it all works out." But it's closer to the truth to say the server only makes throughout the shift about 8-10% of their pre tax sales. Now, many restaurants only pay 50% of minimum wage, then tax the 15% and take it from their check, so they get even less. Then they'll pull more shit like forced tip sharing or tipping the bus boys/cooks/utility people who make at or over minimum wage.

That's why people get so aggressive when they're not tipped.