BMW jerks deserve to be shamed. :P This claim is disputed.
It would be interesting to see stats on aggressive driving by brand. My guess is that BMW drivers would be well near the most aggressive on the list.
Measuring aggressiveness is going to be a measurement of outliers. For everyone weaving through traffic in their BMW without turn signals there's a gray hair putting along. For every Tacoma clogging up the left lane there's a Prius taxi hauling ass to the next fare. I don't think it's a very informative thing to try to measure.