Here are some options depending on the context:
Direct opposites:
* Cruelty: This is the most direct opposite, focusing on causing pain or suffering.
* Meanness: This emphasizes a lack of compassion and a tendency to be unkind.
Other possibilities:
* Rudeness: This emphasizes a lack of consideration and politeness.
* Insensitivity: This focuses on a lack of empathy and understanding.
* Callousness: This emphasizes a lack of concern for others' feelings.
* Heartlessness: This emphasizes a lack of compassion and empathy.
* Indifference: This implies a lack of interest or care about others.
The best opposite for "kindness" depends on the specific situation and the type of unkindness being considered.