I know, I've done this before, but it's so simple I can't help but do it again. Maybe I'll make one every summer forever.
Again, all you need to do is make a rectangle the width of your shoulders and back, and as long as you want it to hang. I just used a basic shell (3dc in one stitch), then sew up the outer edges to make arm holes.
I did a couple of rows of dc with a smaller hook around the arm holes and edges just to give it a nice finish, but that's it.