JMich: The stereotype isn't that German humor is incomprehensible. The stereotype is that Germans have their sense of humor surgically removed.
But yes, would be nice to hear about it from a proper German.
Ah, yes, there's this stereotype too (which is indeed more prevalent), but there's also this other stereotype I've seen on the internet that Germans do have humour, but nobody else understands it (guess 2 similar versions about a particular stereotype can co-exist...). I personally am more inclined to this 2nd version of the stereotype, because, as I've been trying to learn German for the past few years (took a beginner level at the university, and German was offered as a language in my lyceum and took it then -I should really go somewhere more institutionalized though, like Goethe institute, indeed...), I browsed through the internet a few times to find educational resources for German and also to learn more about German culture, and the consensus from non-Germans learning the language was that German humour does exist, but most non-Germans don't get it, because it's a weird kind of humor (I've seen it compared to British black humour, which I indeed do not like much...).
So in short, according to this 2nd stereotype, to someone that doesn't understand German humour, a German person might seem like he doesn't have any humour, because he doesn't have much of the humour non-Germans understand more and prefer (plus, some German humour is untranslatable to other languages because it depends on wordplay)... So, a clarification from a proper German sure would be welcome in that sense (that is, maybe there's some German humour that can be translated well to other languages and understood)...