I don't remember where, I think the reason 25% sticks in my mind is because I usually do 20% and tend not to think about it. I did stop going to restaurants because of it but I would still go to fast food / take outs and then they started requesting tips before they even made the food. The increased in cost on top of the tip felt like small scale extortion - what are you going to do to the food if I don't pay. So now I just cook at home and save a bunch of money and I wonder how many others are doing the same.