What is a social strategy I can use to respond to "How's your PhD going?"

I was surprised when starting my PhD as to how much I get asked this question and how much I fail at answering it. Whenever I attempt an answer, I fumble around and the subject immediately changes after. If I state exactly how it's going, the stress of publishing and intensity of the program comes off overly negative. If I state what I'm working on, I either lose them or bore them.

What's a good social strategy to respond to this question?