This is why the Internet is great: the Wikipedia page listing common misconceptions. Here’s one misconception I recently overheard when I was traveling:
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 jelly 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 usually called ein Pfannkuchen.
I declined to correct the two individuals, though I really wanted to interrupt, mostly because the person relaying the supposed anecdote was extraordinarily smug about it.
(kudos to Kottke for the link)