Dreaming about people they had previously been cruel towards represents revived painful, closed off feelings; where we are able to face what has been hidden and go into new territory without the fear of being hurt and judged.
Dreaming about being cruel is a reflection on the individual. Those who believe they wake in a cruel reality, that they are happy to see themselves or others do cruel things, are not as cruel as they think they are.
Also, when a person dreams of suffering and pain along with feelings of cruelty then it suggests their life continues to hold an emotional weight of desires not being fulfilled.