RORY: Um Dean, I don’t think you two have met. This is Jess. This is Dean.
JESS: Boyfriend?
RORY: Of course.
JESS: Sorry, you didn’t say.
Naturally Jess knows that Dean is Rory’s boyfriend – he must have seen them walking around town together and smooching outside the market numerous times. He probably targeted a prank at the market because he knows Dean works there.
Jess does enjoy letting Dean know that in the two months since he and Rory met, she never bothered to mention Dean’s name or said she had a boyfriend. If Dean doesn’t treat this as a red flag, then he’s not very bright.
The Annotated Gilmore Girls 