It seems to be a little known fact that you can, in fact, crochet with that ruffle yarn that is so popular these days. Personally, I'm not a fan of this kind of yarn. I find it to be a pain in the butt to work with as it tends to curl up on itself at the slightest provocation.
I did find it slightly easier to work with when crocheting than with knitting, though, so there's a plus!
Here's how to do it with Red Heart Sashay yarn using a 6mm hook (it's pretty much the same method for all the yarns of this type... you just need to figure out where to put the hook)
First you need to spread the yarn out - you'll see that it's a net. There's an edge that has some sparkle to it, that's the bottom edge. You will be crocheting with the top edge only.
Along the top edge there is what people call "train tracks" - a series of holes that alternate between big and small.
We will be concerning ourselves only with the large holes. Ignore the small ones.
You don't need a slip knot to start with this yarn, you just insert your hook and off you go. Now, when I start, I fold the end over a bit and work into both layers for about an inch or so. It's not shown in this picture because, frankly, I took that picture and you couldn't see what was going on.
To get the ruffle effect, you simply skip a large hole and go into the next:
That's it. Every time your pattern has you "yarn over", you skip a large hole and insert the hook into the next large hole.
Start with a base chain that is approximately the length of the scarf you want to make (up to 6' long is a safe length for one ball)
Here's what it looks like when you pull that second "large hole" loop through the first:
Here I am, grabbing the next spot, two large holes away:
When you have the length you want, turn and sc in each chain. Now, the chain is hard to see, both in this picture and in real life:
But do your best - only work into one loop of the chain. It's too much of a pain to work it any other way, in my experience.
When you've sc across, turn and slip stitch back down again. And you're done! Finish off by cutting the yarn and pulling the *whole* thing through the loop on your hook. Pull it snug, and then trim the end if you find it's sticking out too much. The end should basically hide itself in the ruffles.