If I was Letterman I would have slammed my head on my desk like 5th times after he said "The Sixteenth Chapel".
Well, I don't know how popular European culture is in North America, but I can forgive Justin for not knowing that there is the Sistine Chapel and to understand 16th one. THough his facial expression, when he didn't get it was priceless^^
And the disrobing part is maybe more the "what the fuck?" reaction, but whatever.
The German one was really unforgivable xD
I don't know about people in North America, but I guess, that education about the nationalsozialism in Germany and the Holocaust is compulsary for almost every student in the world, as it is somehow the most deterrent (or at least the most popular) example for a twisted ideology leading the world into a WW.
(Though I don't think, that the stereotype of the dancing, beer drinking Bavarian wearing lederhosen is any better :-) )
His general knowledge really could be better. His (un)popularity reminds me of Tokio Hotel in Germany a few years ago.
Who knows, maybe it's just some adulthood thing, as soon as such teenage stars are out of their teens, they are forgotten by the majority of the people and only sometimes resurface in some crappy shows together with other B or C movie "starlets" and ex-casting-show-winners from 5 seasons back.
One can always dream...