- Oh, be serious, Charlie Brown.
- No, I mean it.

4 seconds sound clip from the Happy New Year, Charlie Brown! movie soundboard.

You can hear this line at 00:17:24.036 in the VHS version of the movie.

Quote context

[...]

- 'Cause when the music stops, you can't be standing there, if you wanna be a winner.

- You've got to be a winner!

- If you wanna be a winner at... musical chairs. Yeah!

- Come on, Charlie Brown. It's almost midnight. I'll pour you a root beer.

- Thank you, Lucy.

- I've decided next year, I'm going to be a changed person.

- Oh, be serious, Charlie Brown.

- No, I mean it.

- I'm going to be strong and firm.

- Forget it, Charlie Brown. You'll always be wishy-washy.

- Why can't I change just a little bit? I've got it. I'll be wishy one day and washy the next.

- Charlie Brown, I have news for you. You will never...

[...]