Kennedy should have said "Ich bin Berliner" to mean "I am a person from Berlin." By adding the indefinite article ein, his statement implied he was a non-human Berliner, thus "I am a jelly doughnut". The statement was followed by uproarious laughter.
The legend stems from a play on words with Berliner, the name of a doughnut variant filled with jam or plum sauce that is thought to have originated in Berlin. This urban legend is largely unknown in Germany, where Kennedy's speech is considered a landmark in the country's postwar history.
The legend can be deconstructed on a number of points:
While there is a "jam doughnut" variant that is common in Berlin, it is only known as Pfannkuchen (pancake) in the city and nearby regions. The name "Berliner" is based on etymologic travel: other parts of Germany picked up the pastry under the name of Berliner Pfannkuchen (= pancake from Berlin), which in turn has been shortened to Berliner. That name has travelled further abroad and is now known in some English-speaking regions. In the 1960s however the term "Berliner" for the pastry sounded strange to people in Berlin.
There is no grammatical error in Kennedy's statement; the indefinite article does not change its meaning. In German, the statement of origin "Ich bin ein Brandenburger" (I am from Brandenburg) is more common than "Ich bin Brandenburger", but both are correct. The article "ein" can be used as a form of emphasis: it implies "just one of many." As Kennedy did stress the "ein", the usage was, according to German linguist Jürgen Eichhoff ,"not only correct, but the one and only correct way of expressing in German what the President intended to say."
The telling of laughter may stem from an associated incident based on the simultaneous interpretation of his speech from English to German (which is the reason for the many pauses apparent in the audio recordings even that most tapes do not carry the interpreter's voice). After the president said "Ich bin ein Berliner" the first time, he was applauded, and a few seconds later he added jokingly, "I appreciate my interpreter translating my German!" This statement was followed by laughter and applause. That timeline fact is evident, so there was no laughter connected to the German phrase but to the next English phrase.
