My sister acts like this and it's so freaking annoying sometimes I just wanna bitch slap her. I will I admit sometimes I act stupid when I'm messing around but it's obvious I'm messing around, when I'm serious I won't dumb myself down to get someone.
I think it's because if a female lets the male think that he's smarter, or right, then she will be able to get him. 'Get' as in date. I think that's pretty, well, low of them, because I like my girls intellegent. There's no need to dumb yourself down to get a man. If the male really liked you, he wouldn't care if you're more intellegent than him.
That's just how I see it, though. Based on what you had in your blog, it seems that's what she was trying to do-- Let the guy know he was smarter and perhaps, more superior.
I've actually never met a girl that acted dumb and occasionally showed her smart side but that's appalling and pretty embarrassing. Acting dumb is not cute and I have yet to meet a male who doesn't admire a smart girl more than a stupid one.