The way the tips are done now, with the server basically standing over you, watching you put the amount down, I almost feel like it's a mandatory 18% minimum tip--there really didn't feel like there was any comfortable way to go any lower for subjectively "meh" service.
As confrontational as I can tend to be (I coach) that won't be good. I'll tip what my wife and I deem to be fair, but take what you get and move on (I'm sure I'll get flamed for this, oh well...).