I've seen this also. I zeroed out the tip and didn't leave anything. It's not a tip if is it already calculated into the bill. If the server has a problem with that then they should take it up with management.

We have had a manager in Boston complain for 10% tip. :)

Debating the merits of tipping vs. paying more (and thus charging more) is an endless debate without a good answer. There are local customs the world over which impact the way things are done. Those are not changing anytime soon and won't be solved as part of any one meal (if they need solving at all).

Group meals require a bit of diligence for the organizer. Most restaurants are quite clear about whether they add a tip and how much it is. It is also a perfectly fair question to ask when booking, whether the tip goes to the employees and how it is calculated. Most likely, the tip is on the total check, thus including taxes. Once you understand what the deal is, you can make a decision as to whether the restaurant represents good value for what you want. Whether the tab comes to $75 per person including tip or there is no tip, but the price is $75 really makes little difference.

A decent server would have said "tip is already included". She was gaming the system hoping you would not notice and it paid off.