hard as nails

*hard as nails

Cliché [of someone] stern and unyielding. (*Also: as ∼.) Don't try to bargain with Liz. She's as hard as nails. Bob may seem sweet and easily swayed, but in fact he's hard as nails.
See also: hard, nail

hard as nails

Unyielding, callous, unsympathetic, as in Don't ask her for a contribution-she's hard as nails. This expression has replaced the 14th-century simile hard as flint stone and presumably alludes to the rigidity of nails.
See also: hard, nail

hard as nails

If someone is as hard as nails, they are very unsympathetic towards other people and do not show their emotions. He's a shrewd businessman and hard as nails. When necessary she could be as hard as nails. Note: You can use hard-as-nails before a noun. That was his hard-as-nails trade representative, Carla Hills.
See also: hard, nail

hard as nails

1 very hard. 2 (of people) insensitive or callous; without pity.
See also: hard, nail

(as) hard as ˈnails

(of a person) not sensitive or sympathetic: She doesn’t care what happens to anybody. She’s as hard as nails.
See also: hard, nail
References in classic literature ?
And the counsellors--who look as hard as nails mostly--I saw, spared him as much as they could.
I'm fifteen stone, as hard as nails, and play center three-quarter every Saturday for the London Irish.
So she had another dug and a frightful expense it was, and the water as hard as nails.
Teenagers "are facing this pain every day, and someone needs to take an intense stand in defense of them," Fatica writes of his controversial tactics in his book, Hard as Nails (Doubleday).
The company is also strengthening its brand identity by playing on the first Sally Hansen product, Hard as Nails, to continue to promote healthy nails.
For extra strength, you can't beat a coat of Sally Hansen Hard As Nails, pounds 3.