Tipping: What’s Expected?

I recently went to brunch with a couple friends and when it came time to pay the bill, I pulled out my trusty iPhone tip calculator app CheckPlease. Generally speaking, I tend to be a “double the tax” tipper, which in California fares better than it does in Colorado. In California, doubling the tax usually comes out right under 20% and in Colorado just above 15%. Either way I think, not bad. Regardless, because we were splitting the bill multiple ways, and I’m completely inept at doing simple math, I figured the app was appropriate. I put in the total, the amount of people splitting the bill and the 15% as the tip amount. One of my friends immediately pointed out that I had clearly never worked in food service because of the insultingly low 15% tip I had chosen to give. He was right – I’ve never worked in food service, but since when were tips expected and not only that – expected to now be at least 20%?