I think Mercedes drivers are the worst. Usually driven by arseholes that hog the overtaking lane on a motorway at 60mph and then can't decide whether to pull in and let the traffic by or not. This results in them weaving* between the two lanes and scaring the shit out of everyone. VW drivers are becoming fannies too although Seat drivers are making a late bid for fannydom.
I drive an Audi and I always make sure to indicate because I am a considerate, albeit passionate, driver. That and I hate people that don't indicate. Or fail to use the roundabout appropriately.
*by weaving, I mean they don't actually make it into the 'crawler' lane. They go halfway across the dotted line and then swerve back into the overtaking lane just in case.
Also people that brake for no reason.