Kennedy came up with the phrase at the last moment,
as well as the idea to say it in German.
Kennedy asked his interpreter Robert H. Lochner to translate
"I am a Berliner"
only as they walked up the stairs at the Rathaus (City Hall).
With Lochner's help, Kennedy practiced the phrase in the office of then-Mayor Willy Brandt,
and in his own hand made a cue card with
According to an urban legend,
Kennedy allegedly made an embarrassing grammatical error by saying
"Ich bin ein Berliner"
referring to himself not as a citizen of Berlin,
but as a common pastry
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"...
( Wikipedia )