You are all ready for a night out on the town with your best friends when you notice in the mirror, while doing your last check, that your zipper is down. You could have sworn you zipped up your trousers. It isn't your imagination, your zipper did slide down on its own -- it happens sometimes when a well-loved garment's zipper becomes too worn to stay zipped. Don't fret. You can take a few simple steps to keep that zipper from sliding down and salvage your favourite trousers, or any other garment you are fond of, that has a zipper.
Pull the zipper pull all the way to the top of the teeth of the zipper.
Fold the zipper pull down, so it points to the bottom of the zipper.
Press the zipper pull in toward the zipper until it clicks into place to indicate it is locked.
Take a hair elastic and flatten it so there is a loop at either end.
Push one end of the flattened elastic through the hole on the zipper pull, either front-to-back or back-to-front.
Thread the other end of the flattened elastic through the loop on the end you pushed through the zipper and pull to tighten it down on the zipper pull.
Pull the zipper up to the top of the trousers and loop the elastic around the button of the trousers to hold the zipper up. If your trousers don't have a button at the top, skip the hair elastic and secure a safety pin through the zipper, going across the teeth, just beneath the zipper pull to keep it from sliding down.
Open the zipper.
Spray the entire length of the zipper with a generous amount of hairspray being careful not to get the hairspray anywhere else on the garment. The best way to do this is to hold the garment by the zipper allowing the rest of the garment to fall away from the zipper to keep it out of the line of fire.
Spray extra hairspray around the top of the zipper -- the key is to make the zipper sticky. Pull the zipper all the way up and apply more hairspray as needed.