Road Rage....

[speedminded]

n California:

21753. Except when passing on the right is permitted, the driver of an overtaken vehicle shall safely move to the right-hand side of the highway in favor of the overtaking vehicle after an audible signal or a momentary flash of headlights by the overtaking vehicle, and shall not increase the speed of his or her vehicle until completely passed by the overtaking vehicle. This section does not require the driver of an overtaken vehicle to drive on the shoulder of the highway in order to allow the overtaking vehicle to pass.

Are you in California? http://www.dmv.ca.gov/pubs/vctop/d11/vc21753.htm

Also, this below is from Wiki, so not a very credible source, but it's how I feel

Originally Posted by Wikipedia, I know, it's a shitty reference
A driver hoping to pass a slow motorist in the "fast lane" is stuck in an awkward situation. One strategy is to signal a lane change toward the center median. Another is to flash headlights. A third, which sacrifices safety, is to drive very close to the "fast lane" driver's bumper (this is known as tailgating). In Germany it is common to signal a lane change toward the center of the road, as if there were another lane to the left of the "fast lane".
Most commonly, motorists will attempt to overtake the outer car on the inner lane either to continue at a fast pace or to pass a car that is simply going too slow in the passing lane. For high-capacity multilane freeways (three or more lanes per direction), many motorists often pass on the inner lane, largely in response to misuse of the "passing lane" by slower traffic.

Flash to Pass is in Europe only (and California). My European motorcycle had the switch but no US bound European cars have the switch that I have seen.