LORELAI (referring to Dean): Is he dreamy?
RORY: Oh, that’s so Nick at Nite.
Nick at Nite is the programming block that broadcasts every night on the Nickelodeon channel, appealing to a crossover audience of teens and adults. It is notable for showing reruns of old television programs, several of which are later revealed to be ones that Lorelai and Rory (the target demographic) watch regularly. This may be why Rory connects the 1940s teen slang “dreamy” with Nick at Nite: she may have heard it on old TV shows.