How Should I Deal With Internet Trolls?

You cannot win with a troll. Publicly retaliating against them just fuels their c***dish need for attention. There are only 3 reliable ways to deal with trolls, all of which focus on removing their audience, removing their power, and depriving them of the attention they seek.

1.For a casual or emergent troll: completely ignore the person's postings. While it is difficult for most users to to let a troll have the last word, this tactic successfully takes the wind out of a casual troll's sails.
2.For repeating troll offenders: report them to the moderators of the system. If enough people report the toll, this will often prompt the moderators to take action (see number 3 below)
3.Have the moderators take away the troll's ability to post online. This will commonly mean that the troll is kicked from the system, or blocked by IP address. Even better is when the troll is allowed to continue posting, but unbeknownst to him: all of his postings are deleted from everyone else's view. This will lure the troll into wasting his efforts while still feeling proud of his c***dish antics. This moderator move is sometimes called 'muting' or 'bonzo-ing' the offender.