Why Stupid=Popular

I don't know if it is so everywhere, but where I live, stupid means popular.
I have never understood why, when people see you have a brain (incredible!), you immediatly lose whatever chance you had at friendship. With most people, anyway.
In a school enviroment, being smart means you are a nerd. Outside, it means you are boring.

I have some thesis on why that may be:

Thesis number 1: If you are stupid, other people feel exceptionally smart around you. They will spend time with you feeling good about themselves and the greatness of their brains, which makes them like you.
If, on the other hand, you are more intelligent than them, they will feel self-conscious and stupid, which makes you unpopular.

Thesis number 2: If you really are smart, you probably won't be very interested in Paris Hilton's new look. Not finding  in you a shrieking partener, people won't like you.

Thesis number 3: When you hear what stupid subjects some people talk about all the time, you-a smart person-distance yourself from them because of your lack of interest in said subjects. This makes you unpopular.

Thesis number 4: Smart people are actually boring.

Thesis number 5: I have no idea. It's probably part of the contorted human nature. What do you think?