"Joisey" is the way some New Yorkers mispronounced
New Jersey (both leaving out the "New" and pronouncing "Jersey" badly). People who moved to
New Jersey from New York and who prided themselves in not having the extreme accent of some people in their old New York neighborhoods would sometimes ridicule and imitate the way these New Yorkers referred to
New Jersey as "Joisey." These days, some people from other parts of the country, or at least not from New Jersey, mistakenly think that "Joisey" is the way New Jerseyans commonly refer to their state.