in almost every movie the bad girl has darker hair and the good/boring one is blond. why is that?
do you subconsciously believe that too? I have a friend who has dark hair and its true she looks always "sexy / bad" never cute. and she says I could wear the skimpiest clothes in the world and would still be innocent and cute! I thought about this for a while and noticed that actually most good girls in my circle of friends are blond, and the slutty ones all have dark hair lol may be a coincidence though!
The movie question is simple. It's the same as the old black hat / white hat trick used in old westerns. The white hats were generally the heroes, and the black hats were villains. The reason for this was because the white clothes sorta shined and radiated light. It made the hero look all just and pure, and virtuous. Whereas all the black makes the wearer seem shadowy and dark. It's meant to give the impression that this person is mysterious, and perhaps even sinister. This also works with blondes and brunettes. Blond hair can shine and sheen and all the light coming off the light colored hair does what the white hats did. As for your friends, I assume it's either coincidence, or subconscious seeping in what film has been feeding us. There's no good answer for that.
Hair color has nothing to do with it. It must be a coincidence. That or you're subconsciously labeling your friends because movies and media you see portrays girls in that light and therefore you see your friends that way.