a tard and a half
a total disaster of a person who can't do anything right and makes you want to scream
My mom is a tard and a half. She tried to bake a cake and it came out like a brick.
My friend is a tard and a half. He showed up to the party wearing pajamas and brought a sandwich for dinner.
My teacher is a tard and a half. She wrote the wrong answer on the board and didn't notice until class was over.