That's all, you're done! From here on out, your strings will not get pulled out. I don't know how giving credit has to happen, but the only other time...
Some people have an odd sense of humor. Some people find it funny to pull out other people's sweatshirt strings when their not looking. Being in Middle School, this is an extremely prevelent "joke". I love wearing Sweatshirts, especcially ones with strings. In this instructable I turned one of my marching band sweatshirts into an "un-de-string-able" sweatshirt in a few easy steps.
Take a string that you like (I used a golden one from an old sweatshirt that I liked) and thread it through the sweatshirt.
Step 2: Sew the "Stopper Stitch"
Take your sweatshirt (with the strings) and make sure the strings are even. Once this is sewed, it will not be able to change too much without taking out the stitches. Sew through the middle of the hood. Trim the leftover threads.
Step 3: The End
That's all, you're done! From here on out, your strings will not get pulled out. I don't know how giving credit has to happen, but the only other time I've seen this idea of sewing the string so it doesn't come out came from one of my favorite Under Armour sweatshirts.