An invention of the excellently named Tomima Edmark, the Topsy-Tail was the must-have hair accessory for girls in the mid-to-late nineties.
Patented in 1990, what is basically a loop of plastic ended up making over 100 million dollars for the former IBM exectutive's Dallas-based company.

"How does the Topsy-Tail work?"
Well, I'm glad you asked.

The Basic Topsy-Tail Look
Step 1: Grow your hair long enough to put in a ponytail.

Step 2: Find a ponytail holder. Try looking in your junk drawer, or maybe on top of the dresser.

Step 3: Brush your hair.

Step 4: Put your hair in a low ponytail.

Step 5: Insert the long end of the Topsy-Tail into the top of the ponytail, just above the holder, so the loop is sticking out of the back of your head. Make sure it's in the middle of the ponytail or the twist will be lopsided.

Step 6: Stick your fingers through the loop from the head side and grab the ponytail. Pull it through the loop. The ponytail should be sort of pointing up the back of your head.
You look pretty silly right now, so don't get distracted at this point and forget to finish it. It won't win you points at that job interview, trust me.

Step 7: Now for the nifty part. Grab the long end of the Topsy-Tail that is sticking out the bottom of your ponytail, and pull it down and through, bringing the ponytail with it. The hair at the base of the ponytial should be sort of twisted over itself, covering the ponytail holder. Yahoo! You've Topsy-Tailed yourself!

Now you're ready to move on to the more advanced styles, such as The Victorian, The Banded, The Partial, and The Double, instructions for which are all available at www.topsytail.com for your edification. Not to mention the Style of the Week, which as I write this is
The Twisted Spiral
which really sounds more like an amusement park ride or something, but hey, if we can't have adventure in hairstyling, then where can we have it? I ask you.

Of course, you should realize that nowadays it's a little passé to own a Topsy-Tail, or to have an obviously Topsy-Tailed hairstyle, but in about 3 years (at the current rate of fashion recycling) you'll be seeing them in Vogue, I'm sure.