hotboxing is basically keeping any type of outside air from coming into a room/vehicle so the area fills up with weed smoke. From my experience from hotboxing cars, I find that it gets me even higher because every breath you take, you are breathing in smoke that is still lingering in the air. When rolling around in a car, I always do this because after about 3 hits, the entire car is filled with precious, precious weed smoke. try it out sometime rizla if you are safe from the po-po. The best way to do it in a car is like hektik said, just parked somewhere safe and with the lights off. just the system playin some sweet sweet stoner jams. hope you have fun!