Caveat: I am not a German speaker, so I must defer to those who speak German well enough to understand the cultural nuances. As it has been explained to me, "Ich bin Berliner" translates as "I am a resident of Berlin." The moment you add the article "ein" to it, the meaning changes. "Berliner" was a type of jam/jelly doughnut popular at the time, and "Ich bin ein Berliner" translates as "I am a jam/jelly doughnut." German speakers, please weigh in here. I agree with Antilogic that we've seen enough examples to leave this event turned on.