RORY: But if I’m doing my [Philosophy] homework, doesn’t that defeat the point of going to see you play?
DEAN: You can’t glance up in between nihilistic theories?
Nihilism is a philosophy that rejects fundamental aspects of human existence, such as truth, knowledge, morality, values, or meaning. Different nihilist positions hold variously that human values are baseless, that life is meaningless, and that knowledge is impossible. It often takes on a despairing tone.
Another reminder that Dean isn’t as stupid as the writers often make him look, he at least knows the word nihilism. It does seem a little disparaging towards Rory’s studies though, with the subtle implication that her homework is meaningless. He may be feeling a little despairing himself by this stage.