Oca!
Calling someone 'Cabeça Oca' is like yellin' 'You're a dumbass!' but in a way that's not too harsh.
You're a Cabeça Oca! You can't even tie your shoes!
Cabeça Oca! You're so dumb, you don't know what you're doin'!
Cabeça Oca! You're worse than my brother!