I'm Danish, but my girlfriend is German and we rent a car every time we visit her family down there, in Baden-Württemberg. The area around Stuttgart is absolutely awash with big Mercedes and Porsches, for obvious reasons.
(As an aside, if you're ever in the area, go visit Auto & Technik Museum Sinsheim, and prepare to spend a whole day there gawking at awesome old machinery and airplanes)
At first, I found driving there a little bit intimidating. I'm used to Danish roads, where we drive 80km/h rather than 100km/h on most roads, and the speed limits are rather strictly enforced at 110/130km/h on motorways. I'm also used to Danish drivers, who generally accelerate and brake more gently, and generally drive slower cars (due to higher prices/taxes).
In comparison, Germans are more forceful drivers. I wouldn't say "aggressive", because they're much better at stopping for pedestrians at crossings, and yielding the right of way. But they accelerate and brake harder, drive faster in corners and have much more faith in the quality of their roads, and the skills of other drivers.
Once I got used to that difference in behavior, I found it much easier to grok German traffic and fit in.
That said, a BMW X5M passing you at 250+km/h while you're chilling at 160km/h in a rental Opel Corsa is always a little unnerving.