Trolls: don't feed them. For a survey of various kinds of trolls, see Tantek's TrollTaxonomy. I have several Gmail filters which apply a 'troll' tag to emails from these people. Here's what it looks like:

I find highlighting threads with troll participants with a big, red warning label helps to prioritize other, more productive threads as I read mail.

Now that Gmail supports filter importing and exporting, I thought I'd share my troll filters with others.

People I consider to be trolls:

• Robert J Burns (rob@robburns.com)
• John Foliot (foliot@wats.ca, jfoliot@stanford.edu)
• Andy Mabbett (andy@pigsonthewing.org.uk)
• Xah Lee (xahlee@gmail.com, xah@xahlee.org)
• William Loughborough (wloughborough@gmail.com)
• Shelley Powers (shelleyp@burningbird.net, shelley.just@gmail.com)
• Philip TAYLOR (P.Taylor@Rhul.Ac.Uk)
• Leif Halvard Silli (lhs@malform.no)

See also people Tantek considers to be trolls.