I would hardly call getting the already added on 18% screwing the server. That is standard. At most restaurants, in the real world - not WDW, it is up to the server's discretion whether or not to add it on to large parties. It is their gamble, and when they do it, they are pretty much telling you that you do not look like you know how to tip. Sometimes I say something like "Oh, I see you added the gratuity already, too bad" in a joking way. Both myself and DH are in the foodservice industry. WDW is probably a whole different story, though.