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
Jantje	YAHN-tyə	Dutch
Carolina	kah-ro-LEE-nah (Italian, Spanish), ka-roo-LEE-nə (Portuguese), ker-ə-LIEN-ə (English), kar-ə-LIEN-ə (English)	Italian, Spanish, Portuguese, English, Swedish
EydÍS	-	Ancient Scandinavian, Icelandic
Feidhlimidh	-	Irish
Tethys	TEE-thəs (English)	Greek Mythology
Clotilde	klo-TEELD (French)	French, Italian, Portuguese, Spanish