mad as a hatter

He's a very good fellow, but as mad as a hatter. He's called Madman, you know. And never was such a fellow for getting all sorts of rum things about him. He tamed two snakes last half, and used to carry them about in his pocket; and I'll be bound he's got some hedgehogs and rats in his cupboard now, and no one knows what besides.

1857, [Thomas Hughes], chapter III, in Tom Brown’s School Days. […], Cambridge, Cambridgeshire: Macmillan & Co., →OCLC

"I think he’d be as mad as a hatter at your insinuation that he would invite any of his wives, if all I hear of him is true; and what I’ve heard, Wolsey has told me."

1895, John Kendrick Bangs, chapter 7, in A House-Boat on the Styx

I think Adam Wayne, who is as mad as a hatter, worth more than a million of you. But you have the force, and, I admit, the common sense, and he is lost.

1904, Gilbert K[eith] Chesterton, “The Experiment of Mr. Buck”, in The Napoleon of Notting Hill, London; New York, N.Y.: John Lane, The Bodley Head, →OCLC, book III, page 176

Once Lord John passed across his newspaper, upon the margin of which he had written in pencil, "Poor devil! Mad as a hatter." No doubt it was very eccentric, and yet the performance struck me as extraordinarily clever and amusing.

1913, Arthur Conan Doyle, “The Blurring of the Lines”, in The Poison Belt […], London; New York, N.Y.: Hodder and Stoughton, →OCLC, page 31

Sometimes, I feel sure he is as mad as a hatter; and then, just as he is at his maddest, I find there is method in his madness.

1920 October, Agatha Christie, “The Arrest”, in The Mysterious Affair at Styles […], New York, N.Y.; London: Grosset & Dunlap, published March 1927, page 218