Trolls are best ignored.

troll: (v.) (1) To deliberately post derogatory or inflammatory
comments to a community forum, chat room, newsgroup and/or a blog in
order to bait other users into responding.

http://isp.webopedia.com/TERM/T/troll.html

In any large public forum like this there are all kinds or people
and postings. There are trolls, there are flame wars, there are
good people, not so good people, everything. Welcome to politics.
Some smaller groups manage to avoid this stuff but a large public
group is bound to experience it all.

The best response is to ignore/delete trolls and not fan any flames
with more attention. What trolls and flamers want more than
anything is the attention. Ignore them and they go bother someone
else.

More info:

http://members.aol.com/intwg/trolls.htm

Quote from above link:
"Conclusion
Next time you are on a message board and you see a post by somebody
whom you think is a troll, and you feel you must reply, simply write
a follow-up message entitled "Troll Alert" and type only this:

The only way to deal with trolls is to limit your reaction to
reminding others not to respond to trolls.

By posting such a message, you let the troll know that you know what
he is, and that you are not going to get dragged into his twisted
little hobby.

The Internet is a splendidly haphazard collection of both serious
and silly material. Because it is so free, there are bound to be
problems. I think that we can best enjoy it if we deal with
everything that happens online with a wry grin and a ready shrug."