mad as a

(as) mad as a hatter

1. Crazy or deranged; particularly eccentric. I know some of my students think I'm as mad as a hatter because of my weird methods. I'll be mad as a hatter if I have to deal with these screaming toddlers for much longer. My family thinks I'm as mad as a hatter just because I practice a form of alternative medicine using magnetic fields.
2. Particularly cross or angry. Mom was mad as a hatter after I dented her brand-new car. John gets as mad as a hatter when he starts losing. Tiffany will be mad as a hatter when she finds out that her so-called friends started that awful rumor about her.
See also: hatter, mad

(as) mad as a March hare

The phrase alludes to hares' erratic behavior during their breeding season.
1. Crazy or deranged; particularly eccentric. I know some of my students think I'm as mad as a March hare because of my weird methods. I'll be mad as a March hare if I have to deal with these screaming toddlers for much longer. My family thinks I'm as mad as a March hare just because I practice a form of alternative medicine using magnetic fields.
2. Particularly cross or angry. Mom was mad as a March hare after I dented her brand-new car. John gets as mad as a March hare when he starts losing. Tiffany will be mad as a March hare when she finds out that her so-called friends started that awful rumor about her.
See also: hare, mad, march
Farlex Dictionary of Idioms. © 2022 Farlex, Inc, all rights reserved.

mad as a

hatter/March hare
Crazy; mentally deranged.
See also: mad
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
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References in classic literature ?
At the hearin' of this, ye may swear, though, I was as mad as a grasshopper, but I remimbered that I was Sir Pathrick O'Grandison, Barronitt, and that it wasn't althegither gentaal to lit the anger git the upper hand o' the purliteness, so I made light o' the matter and kipt dark, and got quite sociable wid the little chap, and afther a while what did he do but ask me to go wid him to the widdy's, saying he wud give me the feshionable inthroduction to her leddyship.
if it wasn't mesilf thin that was mad as a Kilkenny cat I shud like to be tould who it was!