I have asked myself many times why blonde females have the reputation of being dumb. Is it because blondes on average get more attention from men and get asked out more so that brunettes or black haired women are actually jealous and need something to get even? So they want to put them down and make jokes about them? Maybe, but it's also the men who make "blonde jokes". So that theory isn't waterproof.
Although women know they will be made fun off, they still want to be blonde. Probably for the reason mentioned above.
Personally I don't think the hair-colour has anything to do with intelligence. Most blondes are dyed anyway so they're not naturally blonde. It's stereotyped.
A lot of celebrities are or were blonde and most women want to look like them period.
I'm not one of the many men that prefer blonde. And that has nothing to do with the intelligence issue but everything with the looks.
Videos like this won't help the reputation of blondes but I couldn't resist. Sowwy blonde readers.