mad as crackers - A total nutcase. Like when a kid eats a whole jar of pickles

A total nutcase. Like when a kid eats a whole jar of pickles and then starts screaming at the sky.

My sister’s friend is mad as crackers. She thinks the internet is a real person.

My dog’s owner is mad as crackers. He talks to his dog like it’s a CEO.

My friend’s dad is mad as crackers. He tried to build a spaceship in his garage.