Cut a piece of embroidery floss in your favorite color. It should be about 5" long.
Thread the floss through the stitches on the back pocket of your jeans using the embroidery needle. Start at the first stitch and push the floss up, then pull down through the second stitch.
Tie the floss into a double knot to secure it.
Cut another piece of floss in a different color, thread the needle, and pass it through the second stitch, then pull it down through the third stitch.
Continue in this manner until all stitches in the top stitch line of the pocket are covered in floss.
Brush out to tidy the fringe.
Stabilize the top of your fringe with scotch tape to keep it in place as you work.
Use embroidery scissors to trim the floss to your desired length, creating an even, polished fringe.