*Don't Feed the Troll

Characteristics of a Troll-
A troll usually has little or no interest in contributing to the development of the site in question and is interested in some or all of the following:

    -Deliberately angering people.
    -Breaking the normal flow of debate/discussion.
    -Disrupting the smooth operation of the site.
    -Deliberately being annoying for the sake of being obnoxious. For instance, using abusive names to refer to all the members on the site.
    -Pretending to be profoundly ignorant or stupid, gleaning some weird sense of having "won" when other users subsequently come to believe this.
    -Making itself the main topic of interest or discussion.  

Motives of a Troll-

It is probable that, for the troll, the last point is the most important. To this end it will post deliberately inflammatory messages which generate inflammatory responses; complain about being the victim of the inflammatory responses; endeavor to obtain allies against the discrimination it feels; turn on those same allies, etc. The whole objective of the exercise is to disrupt or make someone do something you wanted them to do for laughs.

If a poster begins to post comments along the lines of, "Can’t you see how stupid you all are?" or "I keep laughing at all of you," there is high probability that the poster is a troll.  

 
How to Spot a Troll-

Usually it is very difficult to tell the difference between a troll and somebody who is simply an asshole. It is important to note that a troll doesn't always resort to insults. Some of them pretend to hold ideals that are unpopular on a particular website or forum.  The best way to spot a troll is to take into consideration how long its posts are. If its posts are short then more than likely you are dealing with a troll. A good troll also doesn't show any signs of anger in their posts, so it would be best to keep an eye out for that too.

Ways to deal with a Troll?

If you feel exceptionally compelled to respond to a troll, don't post long comments. Try to make any responses as short and concise as possible; it's often best to use exceptionally bland statements such as "Thank you for your comments, which we shall give due consideration." Your main objective is to disarm the troll's chances of getting an emotional response from other users, which in turn will hopefully demotivate it until it gives up its attempts. This method is not fool-proof: it can at times achieve the exact opposite results depending on the troll and how you go about doing this.  

 

*Most of this information has been copy pasted from rational wiki, and I am posting it merely as a resource for those during troll season.

Another helpful resource to help you in this battle against trolls is http://www.peorian.com/technology/technology-news/trolls-cyberbullies/1079-how-to-identify-and-defeat-an-internet-troll