The results are skewed by BMW drivers, who are virtually always assholes.
Mercedes drivers are generally gentlemen of style and taste.
Beemers are everywhere, so there's a wide variety of types of drivers, though there is a large subset that tend to be very aggressive.
Mercedes? It's almost always old rich ladies driving a Mercedes, and they usually aren't paying attention to road signs, or anything going on around them (the same goes for female drivers of a nicer Lexus). They're the type that would run someone over, never having seen them, let out an "oh, did I run over something?" and then keep going, only to tell their husbands there might be something wrong with the car when they get home.
Drivers of a Porsche? There has never been a human who drove a Porsche who wasn't a colossal asshat (not just on the road ... in every aspect of their life ... that's why they get a Porsche).
Acura, Infiniti and Audi? No problems.