It's a word use for such kids pretending to be baddies. They would wear brown lipstick, wear baddie stuff and they would end their last sentence with a "grr"
A 'baddie' is a bad bitch. A girly with an attitude, with confidence. Some baddies are Beyonce and Doja Cat. Everyone can be a baddie as long as you have a lot of confidence
"Damn! Mia is a lil' baddie," Jack said. "Yeah, but don't forget that baddie is my sister..." Harry replied.