There is, for instance, the more direct method...
A man brought his German-born neighbour close to tears by twice calling her a schweinhund, a court heard yesterday....which suffers only the slight drawback that a knowledge of German that goes beyond comic books may be essential: the correct word is Schweinehund.
Don't forget that little linking 'e', and always remember that all German nouns, especially the insulting ones, should be capitalised. (Thanks to The Wife for the link.)
The other, more subtle way of insulting the Germans may be observed in an article at the Guardian by Ashley Seager a few days ago.
It's about the impact of the Global Financial Worldwide Totally Scary Economic Thingy (or whatever) on this here place I call home.
So far as it goes, I think Ashley is correct--though not entirely original--in saying that said economic impact is going to be...wait for it...quite severe.
But he manages the very strange feat of suggesting that key characteristics of the German economy (Making High-Quality Things That The World Wants To Buy) and of the German population more generally (Being Somewhat Cautious With Their Money and Not Going Crazily Into Debt) are not the sensible and virtuous things you might have thought and are...instead...somehow...deeply shameful.
I think he should have just come out and used the word Schweinehund.
It would have been friendlier.