If you're posting to have a player blacklisted, make sure to have sufficient evidence. Inappropriately reporting someone may result in your own blacklisting. Don't forget to post in the AC Blacklist thread as well.
If you're posting to warn of a suspicious/annoying player, again, bring evidence (get demos, screenshots, w/e you can legally). Post what happened with a brief description, the evidence, and what you think the outcome should be.
This is to help keep AC free of cheating/fun-killing people. Only post here seriously. Abuse of this means you can't use it.