JESS: Okay, I’m going. Look, man, I really was just dropping off some food, so don’t get all West Side Story on me, okay? [leaves]
West Side Story, previously discussed.
Jess refers to the gang rivalry between two Upper West Side gangs of New York, the Jets (white Americans) and the Sharks (Puerto Ricans). Maria, played by Natalie Wood, is a Puerto Rican girl who has come to New York for an arranged marriage with a man named Chino she does not love. She is drawn to Tony, played by Richard Beymer, a former member of the Jets.
Jess is taunting Dean by hinting that Rory no longer loves him, and like Maria, has fallen for a boy who is off-limits to her. In the film, Chino comes after Tony with a gun during a rumble, and shoots him dead. This is another suggestion that Jess is expecting Dean to become violent with him in order to keep him away from Rory.