Being a computer consultant by day, (Superhero by night) I have the following suggestion to aid in this situation.
Since this board is written in PHP, create a new page that gives a message, (in big letters) that there is NO HACK TALK allowed. When a new user signs up for the forum and they click the "New Post", "Quick Reply" or "Reply" button if there posts count is less than 10 then they get the warning page that has a continue button at the bottom that brings them to the normal page. If they have more that 10 posts, they go right to the reply pages.
I have done most of my web work in ASP, but because PHP is so similar, I could probably do this for you guys if you want.
Just an Idea. It won't eliminate the problem completely, but should get the message across.