A "Jewstring" is basically a "G-String" manufactured specifically for Jews. "Jewstrings" tend to be unexpensive and in some situations very uncomfortable. Typical "G-String's" are built to fit comfortably and at times can cost a fortune! "Jewstrings" were invented so Jews can save money, but still be stylish. They come in lots of sizes and colors. The most popular being "Yiddish Yellow," "Shalom Silver," and "Goy Green."
Guy: "Hey, check it out! That chick's Jewstring is showing."
Girl: "Eww, why are looking at her Jewstring?!"
Guy: "Cause it's totally showing!"
Girl: "You're sick!"
A combination of the words "Jew" and "instincts," Jewstincts usually refer to sound financial decisions. The term generally carries a positive connotation and is applicable to people of Jewish or non-Jewish heritage. It can be used as an insult in the proper context, especially if someone is being Scroogey with his or her money.
Guy 1: Bruh, when you gonna start paying for da weed, too? You always be hittin up on my stash!
Guy 2: Nigga pleez, you straight stuntin! You can pop hundies all you want, but why I gotta throw down Kraft singles when I can get it fo free from you?
Guy 1: Bitch, damn you and yo Jewstincts!