(Sees Rory on the phone)
LORELAI: “And Justin is just so dreamy. He can’t marry Britney, I’ll just cry and cry and cry.”
Lorelai mockingly supplies imaginary dialogue for Rory, based on a stereotype of what teenage girls talk about on the phone. She is referring to singers Justin Timberlake and Britney Spears, who began dating in 1999, and who were frequently rumoured to be engaged. They broke up in 2002 and eventually married other people.
Rory is actually talking to the pizza delivery service.