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!"