be as mad as a hatter

to be crazy

Usage notes: A long time ago, people who made hats used a substance that gave them an illness which made people think they were crazy.

Her brother's as mad as a hatter.

Name	Pronounced	Usage
Heleen	hay-LAY:N	Dutch
Wendelin	VEN-de-leen (German)	German, Dutch, Ancient Germanic
Kusuma	koo-SOO-mah	Indonesian
Jarred	['dʒa:rid]
Meriwether	MER-i-wedh-ər	English (Rare)
Irja	EER-yah	Finnish