RORY: People are different once you get to know them. If you’ll remember, you weren’t too fond of Luke when you first met him.
LORELAI: That’s not true.
RORY: You called him Duke for two years just to make him mad.
A meta-reference to the fact that in the original pilot of Gilmore Girls, the Luke character was named Duke. Amy Sherman-Palladino, the writer for this episode, jokes that must’ve been the teasing nickname Lorelai gave him at first. Luke’s character was originally meant to be a woman named Daisy, so the change from Daisy to Duke seems like a Dukes of Hazzard reference.
Apparently Luke and Lorelai didn’t get along when they first met, and it took two years for Lorelai to call him by his correct name. This sounds awfully similar to the plot line where Tristan keeps calling Rory “Mary” when he first meets her, as a flirtatious tease.
In the world of Gilmore Girls, someone getting your name wrong is a sure sign they secretly like you! As Tristan was originally slated to be Rory’s boyfriend (before the actor went to a different show), it also seems to be a sign you are destined to end up together.