Cherry insults Dally, and does not accept the Coke he tries to buy her.

When Ponyboy meets Cherry at the drive through movie, he thinks she is a nice girl.  Unfortunately, Dally does not have the best manners, especially when it comes to Soc girls.

Cherry does not like Dally’s attention.  She even threatens to call the cops.  When he offers to buy her a drink, she does not warm up to him.

Dally grinned roguishly. "I'm never nice. Want a Coke?" She was mad by then. "I wouldn't drink it if I was starving in the desert. Get lost, hood!" (ch 2, p. 23)

Dally just shrugs and leaves, and Cherry asks Ponyboy if he is going to start messing with them.  Pony would never consider it, of course.  He thinks Cherry is pretty, and even starts to like her. 

The class difference between Cherry and Dally is only one of the issues here.  She does not like his piggish behavior, and that is why she calls him a hood.  He expects her to be a snob, and that is why he teases her.  Neither gives the other a chance.

Once he talks to her, he realizes that as different as they are they have a lot in common.  Both have problems.  Both are thoughtful.  They see the same sunset.