She's hard as nails.

她像钉子一样硬。

The soldier was as hard as nails.

这位战士身体如铁打一般的强健。

They are merciless, with hearts as hard as nails.

他们冷酷无情，铁石心肠。

They offered me a good job at that company but I hear that the boss is as hard as nails.

他们向我提供那家公司的一个很好的职位，但是我听说他们的老板是个很难相处的人。

They offered me a good job at that company but I hear that the boss is as hard as nails. So I've not decided yet.

他们向我提供那家公司的一个很好的职位，但是我听说他们的老板是个很难相处的人。所以我还没决定去不去。