Any instance that pertains to being cheap or overly stingy with money in an extreme manner. Attempts to getting free items can also be used with Johnny Jew. Johnny Jew can be used either as a name or a way to describe a situation.
"I just begged the cashier to give me a free piece of cake for 15 minutes and she did it...JACKPOT!"
"you're a real Johnny Jew"
"I just got Johnny Jew-ed on ebay- the guy sold me the last ticket at a 400% markup."
"The bitch at the counter wouldn't take my coupon, it was only 2 weeks past the expiration date."
-"You're a Johnny Jew"