[WilliamofCarmichael]

“ich bin ein Berliner!”

"I'm a doughnut?"

Wot?

[Lonesome in Massachussets]

I've heard Germans who've taken it both ways. Strictly speaking, “Berliner” in this context should be taken as an adjective, as in “I am American” (German, “Ich bin Amerikaner.”) However, “I am an American” is perfectly grammatical.

“Ich bin ein Berliner” is, at worst, ambiguous and somewhat awkward. It's hard to think the listener would have construed the noun “Berliner” to mean a pastry in context. I remember seeing the speech on TV news at the time and the crowd went wild.

By the way, JFK didn't say he was a Berliner, he said that the proudest words a person could say were once “Sum cives Romanus.” but today they were “Ich bin ein Berliner.” He was praising Berlin for being in the forefront of the struggle for freedom.