The song is about a girl who always got her heartbroken by jerks. She always tried not getting hurt, but in the end she would anyways. Now she's smiling because what a boy did to her, a different girl did to him. A girl broke his heart the same way he broke Christina's, and so now she's celebrating.
She says how there's a million guys like him out there hurting innocent girls, but now she sees how there's girls who are not afraid to break a boy's heart, and she likes that because that way someone will hurt the guys that hurt her, and they'll get their karma.
The song is about a girl who always got her heartbroken by jerks. She always tried not getting hurt, but in the end she would anyways. Now she's smiling because what a boy did to her, a different girl did to him. A girl broke his heart the same way he broke Christina's, and so now she's celebrating. She says how there's a million guys like him out there hurting innocent girls, but now she sees how there's girls who are not afraid to break a boy's heart, and she likes that because that way someone will hurt the guys that hurt her, and they'll get their karma.
I hope my opinion helped xx