The idea came from AOL Instant Messengers warn system. The hack would add a button called warn or something similar, which would be added to the posbit or profile template.
Any member can click the button, and invoke a form similar to the report post to a moderator feature. The form would allow the member to enter a reason, and once submitted, would private message and/or email the member a warning with the reason.
Each member has the ability to warn a particular member once, similar to voting on a poll one time. Once a member reaches x-amount of warnings, they are automatically banned or suspended pending ban authorization from the administrator.