If you're heading home then he'll want to know where from. Oh, a restaurant? Did you have anything to drink? I smell alcohol! Step of the car please. That's one way it can go, and then he can say you were wobbly on your step and now it's a DUI. People have gone to prison for DUIs where they blew a 0.0. You really have to gauge whether the cop is having a bad day and taking it out on you, then figure out how to best respond. I've had very little experience with this, so I can't quite tell you, but you'd want a lawyer's response anyways.