What does 'mean as nails' mean?

The phrase "mean as nails" is an idiomatic expression used to describe someone who is particularly harsh, unkind, or aggressive. It conveys a sense of toughness and lack of compassion, suggesting that the person is blunt or unforgiving in their demeanor. The imagery of nails, which are hard and unyielding, reinforces the idea of a stern or cruel attitude.