You know you're German when. That's like saying you know you are English when you know the difference between you're and your. So, I'd say according to that quite a bunch of people would come across as not German, according to this.
Ten Germans Try To Say The Word "Squirrel" - Digg // Germans can't say the word "squirrel". Though, to be fair, most native English speakers can't say the German word for "squirrel" (eichhörnchen) either.