Twelvies means: Twelvies are people aged 12-14 years old who believe they’re cool. They fucking know all the secrets of the world, particularly girls who believe they’re hot and don crop tops when they go to the dairy. They think it is cool to go out with friends or have fun at parties. They are annoying, irritable and think they’re better than everybody else. The teenie boppers also call them Twelvies. Fucking teenie boppers. (in Community Dictionary, added by Roberto Durham)