It's important to remember that Trolls feed on attention. There is no better way to insure that Trolls will frequent a forum than to feed them. With that in mind here are some simple guidelines to follow to keep your favorite internet fora Troll-free.
1. Report Troll posts using the graphic link,

2. Resist the urge to post a reply stating that you've reported the Troll. Even that reply is enough of a crumb to whet the Troll's appetite and encourage further trolling.
3. Take note of the Troll's user ID. If it's complicated with eccentric spellings, copy it to your clipboard. Open the User CP to the Edit Ignore List page and type or paste the Troll's user ID into the box under Add a Member to Your List... and click on [Okay]. You have now added the Troll to your Ignore List and won't see any of its posts again.
4. Go about your business as if the Troll never existed.
5. The Troll will go away or, if it doesn't, it won't matter because nobody will be reading its posts anyway...
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This site is a bit dated and some the links are dead, but the core is still sound and the advice is good: How to Handle a Troll and Beat Them at Their Own Game