A girl wears gummy bracelets AKA 'Shag Tags', and when a boy breaks one of these bracelets it means that the girl has to do a particular sex act with that boy. If a girl wears these bracelets, depending on the trend, it can show what she is willing to do or what she has experience of doing.
They were originally an 80's accessory but by the 90's they became known as 'shag tags' and in some area's today they are commonly sold as such. Similar ideas have been going around for decades, such as if you pull a ring pull off a can it granted you a kiss, if you peeled a label from a beer bottle it meant you'd get lucky - for the most part these were silly games, not taken seriously. Shag tags are a trend amongst teens all over the world, and like most trends they reappear every few years in different forms.
Different types, colours and thickness's mean different sexual acts, this differs from group to group, but commonly black means full sex, brown means anal, yellow hugging, purple kissing and so on. As the trend takes off stores start to stock different types so the meanings become more complex or the meaning is given more emphasis - e.g. a thicker bracelet may be seen as more of a serious promise of a sex act when broken.
For the most part this trend is a silly fad followed by young teens interested in sex, like giggling at photos of breasts in sex ed classes, however there is serious concern about premature sexualization of young teens.
Girl will say to a boy - 'I'll let you snap my shagtag' - then offer up whatever colour shows what she is willing to do, the boy snaps the shagtag and the girl panics thinking it may mean he expects her to carry through with the promise.