My daughter had this old turtleneck and wanted to change it up.So I cut off the turtle neck and cut out about an inch or even more to the body of the shirt.
Then I opened up the neck piece and divided it in four even strips and sewed them together, end to end, to make a complete circle.
I then did a roll hem with my serger, but you could cut with pinking scissors and not sew at all. I then ran a gathering thread down the center of the strip and gathered. The four seams help you distribute the ruffle evenly around the neck of the t-shirt. Be careful not to stretch the neck when penning the ruffle to the neck.
Sew with a small zig zag over the gathering thread to attach to shirt. Again, be careful not to stretch neck.
The finish product!