I'm a courier, so I see a lot of this, and I've come to several realizations, the most supported being this:
German cars turn people into dicks.
Now I most certainly am NOT blaming the Germans here. Their cars are the best in the world in terms of build quality and fuel economy. It just seems that their AC systems seem to do something to the people driving them, affecting them in a such a way that they lose common sense. They fail to remember rudimentary things like:
Indicating/signalling.
Speed limits.
Using their mirrors.
The purpose of lane dividers.
BMWs, Audis, and Mercs seem to be the most common offenders for being bought by douchebags who shouldn't be allowed on the roads.