i hope it's about... good girls also know how to have fun... being a good girl doesn't mean she's boring... she can go out, have fun, be tough, enjoy her life... so there ain't nothing wrong being a good girl... The rock part means it's kind of rebellious... but in a way that it's inspiring girls who have been looked as boring, geeky, dorky, etc. to come out of their shells, have fun, and show everyone that you can party, you can be sexy, you can have fun without becoming naught, hurtful, nasty or anything that makes you bad... so yeah... I'm thinking it's kind of a song directed to women... or it can be a message to men to that tells 'em good girls are better than bad ones...
so i agree in some posts here... I hope it isn't the "everybody says I'm good, but I'm really a bad girl" kind of song... but who knows? it could even be something like "beware of good girls 'cause they destroy your car" song... Ahahaha...