I don't live in NJ myself, nor have I ever been there.
I've heard numerous times, oftentimes from "New Jerseyians" themselves, jokes and sarcastic remarks relating to people (or males specifically, usually) from New Jersey being very "low-brow" or "uncultured", for example, they allegedly speak in a way which sounds "stupid" or "comical", and they allegedly don't care much about anything or anyone outside New Jersey. Of course, this doesn't apply to every single individual, but apparently to "a large percentage".
In this stereotype, it seems like the guy is oftentimes Italian-American. However, I have also heard a different stereotype about New Jersey where apparently an unusual amount of Jews live there, and in which this is the distinguishing "feature" of New Jersey. But I've also heard that about Long Island (which isn't a state but part of New York) and New York (the state, in general), so I don't know what to make of that.
I guess it's possible for both to be true.
What I'm wondering is why specifically New Jersey was "picked" for this (first) stereotype. That is, among the "Northern" states. I never hear anyone make fun of any other Northern US state in this way. There must be something I'm missing about the history of New Jersey.
I hope that my question is clear enough and doesn't offend anyone. Again, I'm trying to understand why this stereotype exists; I don't have any particular dislike/hate toward New Jersey or the people who live there.