Thanks to Mags and Brian for providing these details!
Rob Fleming, the owner of the used record store in this film, chases a couple of kids who have shoplifted some albums and confronts them outside his shop. The kids throw the records on the ground, Rob picks them up and looks through them, reading aloud the names of the recording artists. Then there is the following dialogue:
ROB: What, are you stealing for other people?
KID: No, those are for us.
ROB: You guys slamming to Joni Mitchell now?
(Contributed by Bob Muller, Mags and Brei)