He means we're all done having loads of fun out here.
5 seconds sound clip from the American Graffiti movie soundboard.
You can hear this line at 01:05:18 in the Blu-ray version of the movie.
Quote context
[...]
- Well, well. Well, well, well. Well, well, how are you, Curt? What a pleasant surprise.
- Congratulations, my boy. We're all proud of you. All of us.
- You know, the Moose Scholarship went to the right boy. You. And we're all proud of you.
- Hey. We're all done out here.
- He means we're all done having loads of fun out here.
- Wonderful. You can have all the fun you want. This place is for fun.
- Curt, before I say goodbye, I hope you'll be taking along with you a little piece of this place.
- No, I won't forget you and you won't forget me.
- Okay. Bye-bye. Okay. Goodbye and good luck. Bye now. Bye. Bye.
[...]