The one that bugs me (currently) is if you go to an actual restaurant where you would leave a tip, they conveniently calculate the tip at the bottom of the receipt - but it's wrong. You tip on the subtotal, not the total including the taxes. I will actually leave less tip if I catch it. Watch out for the mandated tip (usually for large parties) above the total line too. In that case not only would you be tipping twice, but your handily calculated tip at the bottom of the receipt would be calculated after adding in the mandatory tip. Yeah, you'd be tipping on the tip. Now that's a tipping point if ever there was one.