Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
John F. Kennedy's words "Ich bin ein Berliner" are standard German for "I am a Berliner". An urban legend has it that due to his use of the indefinite article ein, Berliner is translated as jam doughnut, and that the population of Berlin was amused by the supposed mistake. The word Berliner is not commonly used in Berlin to refer to the Berliner Pfannkuchen; they are simply called Pfannkuchen. In other parts of Germany, though, the term "Berliner" actually also is used for the product in question, so there is a grain of truth in the myth.