so here's the inspiration:
-liquid stitch-or some other fabric glue-this will help the hole from fraying or stretching excessively
-old shirt (make sure it's pretty long because you'll be cutting strips from the bottom)
and the how:
1. first start by putting a dot of liquid stitch down around the neckline about 1-2" apart. then cut 3 strips from the bottom of your shirt about 1/2-1" thick. it's okay if they're on the thin side because you'll be doubling them anyway. stretch the strips out a little bit-it's basically the same process as all those t-shirt bracelet/headband/necklace/millions of other accessories tutorials. once your glue has dried, cut a small hole in each dot. you can make them pretty small because they'll stretch out later and you def don't want them to be too big. i just made tiny little snips with the tips of scissors.
2. then tie a knot in the end of your 't-shirt yarn'. starting at one side, pull the yarn all the way through the first hole.
3. then take the end and pull it back through the same hole but not completely-leave a small loop.
4. thread the yarn up through the next hole and through the loop you made previously.
5. again, don't pull the thread all the way through-leave a small loop.
6. thread the yarn through the next hole and through the loop. and keep going all around the neckline.
7. when you come to the end, instead of leaving a loop, just pull the yarn all the way through and it should keep the last loop secure.
if you have 2 shirts that are similar colors you could cut up one for the yarn and have a contrasting neckline-you could use the rest of the yarn for other t-shirt yarn accessories.