An incredibly miserly person, the cheapest of the cheap.
In the Western world, Jews are stereotyped as being pennypinching as a whole; in China, people from Shanghai are said to be willing to do anything to save themselves a few yuan. Thus, a Shanghai Jew would be a person so miserly as to be beyond belief.
"Can you believe it? That whole family ordered 5 pitchers of water, asked for bread 4 times, & they all got just soups or salads...and then only left me a dollar tip. What a bunch of Shanghai Jews."
"I told my landlord the heat wasn't working right. You know what the little Shanghai Jew did? Came in, turned off the radiator, handed me one of those little ceramic heaters, & left. That was 2 weeks ago.