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
Marquise	mahr-KEE	African American (Modern)
Koloman	KO-lo-mahn (German)	German (Rare), Slovak
Errol	['erəl]
PaŠKo	-	Croatian
Steen	-	Danish
Csenge	CHENG-ge	Hungarian