- Dumb-bunny?
- That's slang for mentally retarded American girls, like me.

7 seconds sound clip from the The High and the Mighty (1954) movie soundboard.

You can hear this line at 00:56:57 in the DVD version of the movie.

Quote context

[...]

- Here is a letter to my brother in English and I cannot remember this word.

- It is that thing soldiers wear at the end of their guns, like a sword?

- Bayonet?

- Ah, yes. I am so very stupid. Thank you. I am embarrassed.

- Anyone who can write and read more than one language should never be embarrassed.

- Being the original dumb-bunny, I can barely write my own.

- Dumb-bunny?

- That's slang for mentally retarded American girls, like me.

- Dumb-bunny. Dumb-bunny.

- How delightful! I must tell my brother of this.

- You tell him you met the number one stupid rabbit. If he knows any American girls, he'll understand.

- Now I'll get your dinner.

[...]