I've recently been convicted that I need to change my tipping habits. I've been a server before - I know that servers make around 1/3 of the minimum wage that other people earn. I've always (to my wife's chagrine), had a commitment to high tipping. If service is neither laudable nor horrible, I usually leave 15%. Meaning, if they did the job poorly, but had a really good, helpful attitude; or if they were efficient, but had a bad attitude, I leave what I consider to be "the minimum". If service is excellent, I tip 18-20% or more, depending on the setting, the price of the bill, and a number of other random factors.
However, I've always thought (even with my experience waiting tables) that it is my duty both as an American citizen and a consumer to tip poorly if the service is deplorable. When I worked as a server, I felt that if I couldn't do my job well, I didn't deserve the tip. When I tip low for bad service, I have the ability to send a message that "yes, you sucked at this, and I'm making my opinion known." I understand that messages are not always received as the giver intends, but that's beside the point I'm trying to make.
The issue here is, I am first and foremost the citizen of another kingdom. As such, I need to be living by the rules of that kingdom. I need to remember who I'm representing, and what kind of message I need to be sending with my actions. I think if we look at the life of Jesus and the example He set, it's easy to see what kind of message we need to send.
I've rethought my position on tipping, and I think that I'll still be tipping high if I really like the service; but (again, to my wife's chagrine), I won't be tipping low if I don't.