LiveJournal's Abuse Team is responsible for the enforcement of LiveJournal's User Agreement.
If you're having problems with another user, or believe that someone is violating the User Agreement, you can make a report to the LiveJournal Abuse Team. Information on how to make a report is found in How do I contact the Abuse Team? Please read this FAQ before proceeding to the Abuse Report Form.
Information on LiveJournal's abuse policies can be found at Abuse Policies and Procedures.
If you're interested in applying for the LiveJournal Abuse Team, information on the process can be found in the userinfo of lj_abuse.