Sharp and Cutting:
* "He was as sharp as a serpent's tongue, his words leaving wounds that stung."
* "Her voice was like a knife, slicing through the air and leaving a trail of hurt in its wake."
Cold and Unfeeling:
* "His heart was as cold as ice, devoid of empathy or compassion."
* "She was like a stone, unmoved by the suffering of others."
Dangerous and Predatory:
* "He was like a wolf in sheep's clothing, hiding his cruelty beneath a charming facade."
* "She was as dangerous as a viper, striking with sudden and deadly venom."
Vicious and Unpredictable:
* "His anger was like a storm, unpredictable and destructive."
* "She was as wild as a hurricane, leaving a path of wreckage in her wake."
Self-Centered and Arrogant:
* "He was like a peacock, strutting around with his feathers puffed up, oblivious to the needs of others."
* "She was as vain as a narcissist, seeing herself as the center of the universe."
The best simile will depend on the specific kind of meanness you want to portray.