psychopath — a person with a psychopathic personality, which manifests as amoral and antisocial behavior, lack of ability to love or establish meaningful personal relationships, extreme egocentricity, failure to learn from experience, etc.
sociopath — a person with a psychopathic personality whose behavior is antisocial, often criminal, and who lacks a sense of moral responsibility or social conscience.
troublemaker — a person who causes difficulties, distress, worry, etc., for others, especially one who does so habitually as a matter of malice.