A relatively new phenomenon, soda condom bracelets became popular during the summer of 2001, and subsequently enjoyed a second wave of popularity as teens returned to school and taught other teens of the soda condom.
Quite simply, a soda condom comes from a soda bottle. Get a bottle of coke, open it, chuck the bottle, keep the cap. Inside the top of the cap should be a pale blue circle of plastic, under which, if applicable, a message regarding the soda company's contest should be printed (usually, "Sorry Play Again Drink Coke"). On coke bottles, you can use your nails to remove the soda condom from the inside of the cap with some fairly basic finger acrobatics. It's important to note that if you have an alternative soda bottle, it's common that although the soda condom will be present, it will be fastened to the inside of the cap. Don't even try, it's not going to happen.
Once removed, the soda condom is a fairly sheer, light blue circle of plastic, which someone decided resembled a condom (the similarities begin and end there). Around the edge of the circle there's a border of plastic about 3/16 inch thick and divided in two by a darker line.
To make the bracelet, begin by making a hole in the center plastic: most kids will fold, bite the center, unfold, then push their thumb through the center, others prefer to fold, use scissors to make a slit, unfold, and push their thumb through. For most, it's just a matter of convenience. Once you've made the hole in the center, take hold of a section of the center between your thumb and forefinger, and pull so that the center begins to detach from the ring around it. If you continue to pull in a circular motion, the rest of the center will continue to pull away from the sides, all around the ring.
Once the center has been removed from the ring, (and make sure that it's all removed, because any leftover pieces will cause the rest of the bracelet to not stretch properly), you have to go set to the task of stretching it. Some people can do this in 15 seconds and have it come out perfect; other's will mull over one for 15 minutes, at the end of which they're stretch just a little too much, and the ring will snap. My favorite method is to extend my index and middle fingers from each hand so that my palms are facing away from eachother, insert my fingers in the ring, and pull once. After that, I rotate the ring and pull again, this time on a different part of the ring. I repeat this until (and beginners never believe that this happens) the ring becomes large enough to slip over my hand and onto my wrist.
Don't try to make the ring too large, or else you'll just end up without a lot of snapped bracelets. I used to wear about 15 of these, and the majority of them were forced over my hand, felt snug on my wrist, and I had to stretch slightly as I wore them later on (yes, some broke then, too). Also, there's no need to make the bracelet large enough to easily slip on and off. Most people wear their soda condom bracelets all the time, through showers and sleeping, because they dry quickly and you can barely feel them.
I recently learned from a friend that while American soda condoms are pale blue, soda condoms in Israel are dark blue. Anyone out there with access to international soda bottles, if you see a difference, please /msg me!