Well, to be fair, the IRS considers the average tip to be 8% for taxation purposes.

The whole "I get taxed whether you tip me or not", "I have to pay to serve you if you don't tip"? No, not so much. If you can show (there's even a hugely burdensome IRS form that might take as much as 3-4 minutes a month for cash tips) that you earned less than that 8% average, then that's what you get taxed. But most servers don't want to fill that form out, because they get ... rather more than that, and are being undertaxed already.