1
general::
Also, mad as a March hare. Crazy, demented, as in She is throwing out all his clothes; she's mad as a hatter. This expression, dating from the early 1800s, alludes to exposure to the chemicals formerly used in making felt hats, which caused tremors and other nervous symptoms. The variant, dating from the 14th century, alludes to the crazy behavior of hares during rutting season, mistakenly thought to be only in March.
American Heritage Idioms
2
general::
Phrase(s): *mad as a hatter [and] *mad as a march hare
1. crazy. (Alludes to the crazy characters in Lewis Carroll’s Alice’s Adventures in Wonderland. *Also: as ~.) • Poor old John is as mad as a hatter. • All these screaming children are driving me mad as a hatter. 2. angry. (This is a misunderstanding of mad in the first sense. *Also: as ~.) • You make me so angry! I’m as mad as a hatter. • John can’t control his temper. He’s always mad as a hatter.
McGrawhill's American Idioms And Phrasal Verbs