Yes, you can be arrested for DUI for just sitting in the car. If you have been drinking and feel that you may be over the limit (.08 BAC) do not get behind the wheel of a car, even if the motor is not running. The law is APC or actual physical control, and the theory is that if you have the ability to operate the vehicle, by being behind the wheel and having the keys, then you are considered to be in actual physical control of the vehicle. If you had too much to drink dont take a nap in the car, you can get a DUI for being asleep in the car too. I remember one time a client had too much to drink, and decided to lock up her car and leave it at the bar, and ride home with friends. She went out to lock up the car and get her purse, and as she opened the drivers side door with the keys in her hand, she was arrested and charged with DUI under the actual physical control law, and ended up being convicted. If you had too much to drink, do not go anywhere near your car, and give the keys to someone else.
Be Safe Out There.