I'm assuming as long as your engine is off that you can drink in the car. For example, you can be drunk as shit in your car... just don't put the key in the ignition. That's the point that they can hit you for DUI, at least here. In dallas I think you need to be photographed firing your guns off in the air yosemite sam style while someone holds a beer bong to your mouth for any kind of drunk driving conviction.