Someone who constantly compares everything to New York City in an attempt to appear cooler than the situation at hand. Whether the person is from New York or not is irrelevant.
A New Dorker is never truly satisfied with their surroundings. Even when in Brooklyn, they will play-up Manhattan. The idea is to compare every situation with something they hope their audience will view as "bigger and better".
This attitude culminates in comparing Manhattan to a European city that the New Dorker hopes their audience has never been, as to avoid detection and conjecture.
i.e. "Yeah, Manhattan is a lot of fun but its not like it used to be... yawn... Barcelona is way better, they don't start partying until 2am on a Monday morning"
Not relegated to nightlife, New Dorkers belittle the sports events, urban landscape, music venues, restaurants, and culture of any smaller city with which they are unfamiliar with or situations which they find intimidating.
They fail to realize that most of their reasoning is simply contingent on New York's large population and not indicative of the quality of the people or space.
Ironically, New Dorkers often turn out to be the most boring people when you do end up partying with them in Manhattan.
Jake: "Wow... I am having a great time, this club is awesome, the people in this city are really cool"
Jill: "eh... in New York the clubs have like 2,000 people in them, this club only has a 1000"
Joe: "Yeah, I thought it was going to look bigger, I guess I'm just used to the New York skyline you know... this looks small"
Jake: You are a bunch of New Dorkers