- What do you mean by that?
- My mistake.
- Decidedly. You're insulting.

5 seconds sound clip from the The Philadelphia Story movie soundboard.

You can hear this line at 01:14:47 in the Blu-ray version of the movie.

Quote context

[...]

- What have classes to do with it? What do they matter, except for the people in them?

- George comes from the so-called lower class, Dexter from the upper. Well?

- Mac, the night watchman, is a prince among men.

- Uncle Willie is a pincher.

- Upper and lower, my eye. I'll take the lower, thanks.

- If you can't get a drawing room.

- What do you mean by that?

- My mistake.

- Decidedly. You're insulting.

- I'm sorry.

- Oh, don't apologize.

- Well, who's apologizing?

- I never knew such a man.

- You wouldn't be likely to, dear, not from where you sit.

- Talk about arrogance.

- Tracy.

- What do you want?

- You're wonderful.

[...]