Commenting when you are angry.
threatening to ban the user. You do not have that authority, nor is that the purpose of the Reporting system.
Calling any user a thief outside of linking FAQ# 8 (or similar) unless they are intentionally claming ownership of the piece in question or you are the owner of the original piece.
Directly saying the user stupid, retarded, pathetic, etc.
using unprovoked curse words.
Spamming the "You Fail, Please Die" PLZ or similar messages.
Equating the failure to read, understand, or type proper English as being stupid, ignorant, or blind.
Stooping to a Troll's level.
Telling anyone they need to "learn how to draw" or "get a life".
Taking anything anyone says about you via the Internet personally.
...Telling a policy violator they should "delete" or "de-activate" their profile--unless they specifically ask how to do so. (In which case link to FAQ 1