I don't like tipping for those situations where it's unclear how much is appropriate, for instance grocery delivery at the supermarket says their employees won't take tips but then you talk to the delivery person and they say that it's bullshit, people tip anywhere from $1 to $50 at Christmas. What am I supposed to do? Tip a percentage of my groceries? That's ridiculous. Nobody on the receiving end will honestly tell you how much to tip, because they want you to overestimate it.

But when it's clear what to do, like in restaurants and cabs, I'm happy to tip a percentage.