If he is, I'm a banana split.
4 seconds sound clip from the Meet John Doe (1941) movie soundboard.
You can hear this line at 01:52:28 in the DVD version of the movie.
Quote context
[...]
- I'm watching the side door. Colonel's out front, so stop worrying.
- Why Ann!
- If this isn't the craziest, the battiest, the looniest wild goose chase I ever heard of.
- Shut up, Bert. Sourpuss is right.
- If he is, I'm a banana split.
- That man's gonna be on that roof.
- Don't ask me how I know. I just know. And you know it as well as you do.
- I don't think he was any fake. Not with that face. And anyway, what he stood for wasn't a fake.
[...]