The rivalry and mutual distaste between New York and New Jersey is long and complicated to explain. Suffice it to say that New Yorkers tend to look down on New Jersey citizens.
This animosity is so pervasive that even Futurama has made jokes about it.
In order to amuse or mildly offend a New York-based guest, Joe will utilize this gag in some form:
Joe: Oh, I'm from New York too!
Guest: Oh, yeah?
Joe: Yeah! I'm from New Jersey!Some guests will play nice, but others will express a hilarious amount of disgust.