Some blog comments are easy to deal with. They praise you to the heavens, share a related story or gently offer a different perspective... that is, they're a positive part of the conversation. You thank, you respond (or they're comment spam, in which case you report them to Mollom or Akismet and then delete) and the circle of life continues.
But other comments are hard. They get your back up. They seem to question not just your argument but your integrity. The more you read them, the clearer it becomes that they were written by evil, evil people. And with your fight-or-flight mechanism firmly in gear, you write a blistering reply...