According to a new psychological study reported in Nature, a car bumper sticker as innocuous as “Jesus Saves” or “My honor student is a cam whore” are among a few of the indications that the driver is more susceptible to road rage than drivers with no bumper stickers or other bling to personalize the vehicle. So those people with dashboard toys or custom paint jobs for instance are subconsciously marking their car as a very personal space or property.
Coupled with the fact that roads are being over populated will lead to the normal human instinct of increased territorial aggression (this applies to other animals suffering from over population as well). They are more apt to take offense at even the slightest infringement upon what they deem as their space on the road when other drivers are too close or cut them off. Their feeling of having a personal space violated can cause the territorial individual to respond with aggression, hence road rage.
My theory based on that study then goes that if you’re going to cut someone off, take a peek at their car first and only go after the timid or more passive, less territorial drivers, with no car adornments. Those are the people treating the vehicle as a pure means of transportation between two points and less likely to retaliate.