You got no brains ! (But it doesn't always means you are stupid)

Whenever we call people "brainless", "brain dead", "your brain is filled with water/hay", we are trying to imply that they are stupid.

However, there are cases where having an empty brain doesn't make you stupid or retarded.

So there is 44 year old man who has almost no brain but is still miraculously, leading a normal live. FOXNews article here.

For the wordly people, read this for more insight on brains ...
you don't need a brain..it's a no-brainer