mad as a hatter

pähkähullu demented Demented or crazy.
1857, w:Thomas Hughes|Thomas Hughes, Tom Browns Schooldays'', Part II, chapter 3,

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.

"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."

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.

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.

If you ask me that woman's as mad as a hatter.