General:
* Unkind: A more neutral term for someone who is not considerate of others' feelings.
* Cruel: This implies a deliberate intention to cause harm or pain.
* Nasty: This describes someone who is unpleasant and disagreeable.
* Rude: This refers to someone who is impolite or disrespectful.
* Inconsiderate: This describes someone who does not think about the impact of their actions on others.
* Unpleasant: This is a general term for someone who is not enjoyable to be around.
More specific:
* Vicious: This describes someone who is cruel and violent.
* Malicious: This implies a deliberate intent to cause harm or damage.
* Spiteful: This describes someone who wants to hurt others because of anger or resentment.
* Bitterly: This describes someone who is resentful and bitter.
* Stingy: This describes someone who is unwilling to share or give.
* Miserable: This describes someone who is unhappy and unpleasant.
Informal:
* Awful: This is a general term for something unpleasant or bad.
* Terrible: This is another general term for something unpleasant or bad.
* Bad: This is a simple and straightforward term for something unpleasant.
The best word to use will depend on the specific situation and the level of formality required.