I'm just a random "old lady" as far as my kids are concerned, but I actually talked about this with my 20-year-old and his girlfriend the other day. They explained that it's mostly a joke, with a few people doing it for kicks and to get noticed on social media. However, they also likened it to prior generations who chewed on pencil erasers and such, and then pointed out how many delicious-looking non-edible things there are nowadays. Like, pencil grips, apparently.