Mental disorder resulting from living in New Jersey for way too long; characterized by a strongly depressed demeanor, negative disposition about everything, and a general malaise of pessimism about future events.
A downhill spiral attitude in which one believes one is living in dystopia - prompted by the fact that one lives in New Jersey, where nobody smiles.
Joey: "This concert probably won't be that good. I doubt it will be worth it"
Jimmy: "Dude, what do you have Jerseyitis, this concert at PNC Bank Art Center's gonna rock."