Are guys truly attracted to brainless bimbos?

so me and my best friend are polar opposites. The main thing is our brains though. I'm quite intelligent and she...not so much. But all the guys like her and I do not understand why. She's the same age as me, but a year and a half behind in schooling because she failed so many classes. Guys don't like me and people say it's because guys don't like girls who threaten them smarts wise. They say guys are intimidated and prefer girls who don't know much, but I don't understand why. Wouldn't it be better to have a smart girl who could actually hold a conversation with you?
Are guys truly attracted to brainless bimbos?
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