A piece of work
A person who's so dumb and clueless that you can't believe they're still alive. They make you want to scream into a pillow.
My cousin is a piece of work. He doesn't know what the word 'common sense' means.
My neighbor is a piece of work. He thinks the sky is made of chocolate.
My friend is a piece of work. He tried to eat a whole pizza in one bite and cried like a baby.