Very poor German. I.e., most of the stuff that foreigners hate (der, die, das, ein, einen, einem etc.) causes major headaches for them as well.
Is that really true for third generation immigrants as well? 
I wouldn't be surprised that they had their own sociolect/slang - but not knowing basic grammar is a different matter. Something must really have gone wrong in Germany's integration policies.
I assume we're actually talking about a dialect of German spoken in immigrant communities which lacks some features of the standard, a bit like Chicano English.
