This person keeps flashing his lights at you. Because it's the morning rush hour, you can't change lanes fast enough, so this driver whips around your car, cuts you off, then slams his breaks on, causing you to nearly tail end his car. Some kind of personality altering spell overcomes some people as soon as they get behind the wheel of an automobile. They seem to feel that they are invincible, and that they are the master of the freeway, and if anyone dares to get in their way, they will pay a heavy price. The price that an alleged offender will pay could possibly be their lives.
Some people do carry guns.
No matter how obnoxious the other driver is, don't retaliate. Making an obscene gesture will only make matters worse, and could lead to this person getting even more violent. Just try to safely get away from the obnoxious person. If a rager is following you, either try to lose him safely, or pull into a police station. While there, fill out a report on the driver.