An administrator can repair damage made by a malicious user more quickly than other users: if someone is making multiple damaging edits it will be easier for you to report them than try to repair everything yourself. To see whether a user is making many damaging edits click their username and then User contributions.
However, administrators, or other experienced users, may be willing to informally offer an opinion if you ask them privately (for example, via user talk page).
This is done by stewards and only on the request of the Arbitration Committee or on request from the affected administrator, or, in emergency cases only, by developers.