mad as a hatter
idiomPart ofhatter
mad as a hatter — idiom
1. behaving in a crazy or very silly way; extremely eccentric.
1.idiom
Definition
behaving in a crazy or very silly way; extremely eccentric.
Example
Grandpa tells the same wild stories every time we visit — he's mad as a hatter, but we love him.
The main character of the novel is an inventor who is mad as a hatter, building flying machines in his tool shed.