There are, oh, two big plastic storage boxes' worth of thrift store sweaters waiting in the craft room to be given new life, and — miracle of miracles — I actually remembered to dip into them when I was searching for shawl yarn. Therefore this:
...turned into this:
No longer a sweater.
Which is about 716 yards of some kind of synthetic-fiber ribbon yarn. Unfortunately, the content tag was cut out of the original sweater (although the sewn-in ends of it were still there for me to rip out before I could reclaim the yarn ... grumble grumble), so I can't be sure what synthetic fiber it is without doing other tests, which I probably won't bother with. ;)
As I've never hairpin-crocheted with synthetic-fiber ribbon yarn, I have no clue what the end product will look like. It could turn out monstrously icky. I'll find out in the coming days, it seems...