1. Ignore them. Do not take the bait. Let them be. Advise your other readers to ignore him/her. Trolls can not abide being ignored. Leave them alone and they'll go home.
2. Pray for them. Respond in the commbox (either yours or someone elses) by printing out a prayer. Most trolls on Catholic Blogs or even Blogs by Catholics are not Catholic, so pray for them using especially a prayer which invokes the concept of having the Saints pray for us, or my favourite Come Holy Spirit, Creator, Come This particular mode of troll treatment may not remove the troll, but forces the Troll to actually read the prayer, and having read the prayer, it is almost reciting the prayer. And if the Troll is an atheist they won't want to be drawn into that.
3. Recite/Type Proverbs 6:6-12. This proverbs cites those characteristics which God dislikes as well as the one He destests: The soul that sows discord among others.
These are my ideas for dealing with trolls, if you have some other ways of dealing with trolls, other than just delete them before they can taint your commbox, please list in comments
Scripture to keep in mind
Six things there are, which the Lord hateth, and the seventh his soul detesteth:  Haughty eyes, a lying tongue, hands that shed innocent blood,  A heart that deviseth wicked plots, feet that are swift to run into mischief, A deceitful witness that uttereth lies, and him that soweth discord among brethren.  My son, keep the commandments of thy father, and forsake not the law of thy mother. ***Cf:Douay-Rheims Proverbs 6: 16-20
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