These are said to be 'Make-out' bracelets, and when someone brakes one of of you, you make out with them.
Person B: Oops! Lets go make out!
Person A: Okay!
When the top of a soda bottle cap's blue seal is taken out. Then the middle is removed, and the bracelet is stretched to fit around one's wrist.
If you're wearing one and someone rips it off, it means you have to do the dirty with them.