What do you mean, how do I know?
4 seconds sound clip from the Grease (1978) movie soundboard.
You can hear this line at 01:45:13 in the Blu-ray version of the movie.
Quote context
[...]
- Oh, look! All the gang's together!
- What are we gonna do after graduation?
- Yeah. Maybe we'll never see each other again.
- What do you mean, how do I know?
- We go together like rama lama lama ka dinga da ding-dong.
- Remembered forever as shoo-bop sha wadda-wadda yippity boom de-boom.
- Chang chang changitty chang-shoo-bop. That's the way it should be.
[...]