The Jelly Doughnut Urban Legend
On June 26, 1963 U.S. President John F. Kennedy gave a speech in West Berlin where he used the phrase Ich bin ein Berliner. The speech was moving and historically important at a time when Berlin was divided and JFK was making the point that being free is something to take pride in and freedom is a precious right, to be guarded and defended by all people.
Unfortunately the speech was undermined slightly by an Urban Legend that sprung up that the phrase "Ich bin ein Berliner!" did not mean JFK was proud to be a citizen of Berlin on that day, but rather he was proud to be a jelly doughnut.
Turns out that is not the case - citizens of Berlin do refer to themselves as Berliners, and the phrase was grammatically correct. It's a weird urban legend that found it's way into the New York Times and into popular culture.