- Yeah, well, I'm busy.
- Yeah, doing what?
- Washing my hair.

3 seconds sound clip from the Back to the Future Part II movie soundboard.

You can hear this line at 01:06:40.529 in the Blu-ray version of the movie.

Quote context

[...]

- Let me see. Oh! It's perfect, Lorraine. Oh, look at it! You're going to look so good!

- Well, lookey what we have here.

- Hey, nice dress, Lorraine. Although, I think you'd look better wearing nothing at all.

- Why don't you take a long walk off a short pier?

- Hey, listen, Lorraine. There's that dance at school tonight, right. Now that my car's all fixed, I figure I'd cut you a break, and give you the honor of going with the best-looking guy in school.

- Yeah, well, I'm busy.

- Yeah, doing what?

- Washing my hair.

- That's about as funny as a screen door on a battleship.

- Screen door on a submarine, you dork.

- Look, Biff, somebody already asked me to the dance.

- Who? That bug George McFly?

- I'm going with Calvin Klein, okay?

- Calvin Klein? No, it's not okay. You're going with me, understand?

- Get your cooties off me!

[...]