The following response is for general information purposes only and is not to be construed as legal advice.
Below is the statute which pertains to this offense. The short answer to your question is that the person who is in possession of the open container (i.e. back-seat passenger with beer in cup holder next to him) will be charged with the offense as well as the driver of the vehicle in which there is an open container IF the driver has consumed alcohol and the alcohol is still in the driver's body. The passenger area of the vehicle is defined in the statute as "the area designed to seat the driver and passengers and any area within the reach of a seated driver or passenger, including the glove compartment." I have provide a link to an article written by the North Carolina School of Government which sheds some light on this topic.
§ 20-138.7. Transporting an open container of alcoholic beverage.
(a) Offense. - No person shall drive a motor vehicle on a highway or the right-of-way of a highway:
(1) While there is an alcoholic beverage in the passenger area in other than the unopened manufacturer's original container; and
(2) While the driver is consuming alcohol or while alcohol remains in the driver's body.
(a1) Offense. - No person shall possess an alcoholic beverage other than in the unopened manufacturer's original container, or consume an alcoholic beverage, in the passenger area of a motor vehicle while the motor vehicle is on a highway or the right-of-way of a highway. For purposes of this subsection, only the person who possesses or consumes an alcoholic beverage in violation of this subsection shall be charged with this offense.
(f) Definitions. - If the seal on a container of alcoholic beverages has been broken, it is opened within the meaning of this section. For purposes of this section, "passenger area of a motor vehicle" means the area designed to seat the driver and passengers and any area within the reach of a seated driver or passenger, including the glove compartment. The area of the trunk or the area behind the last upright back seat of a station wagon, hatchback, or similar vehicle shall not be considered part of the passenger area. The term "alcoholic beverage" is as defined in G.S. 18B-101(4).
Answered on Apr 11th, 2012 at 4:25 PM