Its personal choice actually. If they think it makes them look cool then why cant they do it? Its like sm people think they look nice in a chicken-beckham hairstyle, but we all think it looks like crap. No offence.

Its like wearing low cut socks, i see so many sec school kids wearing ankle socks. These kids will just grow out of it one day.
Why do you care so much anyway, if you got an issue with that, go approach them loh, or complain to their school. Bet they wont even care if you are looking at them not, if you want to think otherwise then I think smthing is really wrong with you.