The poisoning the well fallacy is a form of ad hominem argument: that is, it is directed against the person, rather than his arguments. Poisoning the well occurs when a debater attempts to bias the audience against his opponent by presenting negative, and probably unrelated, information about him.
I frequent the conservative news/chat forum Free Republic. Occasionally, someone will post an urban legend as news. Inevitably, another poster will point out that the rumour was debunked at snopes.com, the Urban Legends Reference Pages; inevitably, someone else will dismiss the snopes research because the site is "liberal." At this point, it has become irrelevant that snopes.com is one of the better-researched sites on the Web. Conservatives would not want to associate with their liberal views, thus it's best just to ignore the whole site.
Today on the CARM KJV-only forum, which is rapidly becoming my new favourite repository of all bad KJV-only arguments, an exchange with poster "JDS" began with him saying, in response to a statement that KJV-onlyism was a false way:
No, it is the narrow way and the strait gate. (Source)
To which I responded (and yes, admittedly used a little more snark than the author of a fallacies blog might be entitled to):
Oh, good grief. Jesus was speaking of himself as the way, not the KJV.
Do you have so little respect for the sacred that you can never treat the Bible with the care it deserves? Your interpretations are universally pitiful. (Source)
(Matthew 7:13 may, at some point, make it into my "eisegesis" category, if and when I get around to one.)
JDS responded thusly:
This from a man who thinks John 6:44 & John 15:16 applies to himself and whose salvation depends on it.
give [sic] me a break please. (Source)
What an odd response. Some context will help. JDS, in addition to being rabidly KJV-onlyist, is rabidly anti-Calvinist. By contrast, I have never made a secret of my Calvinist theological leanings, and in fact on CARM my user avatar consists of the word "REFORMED," that being the most concise summary of my beliefs from the small pool of avatars the site makes available. John 6:44 and 15:13 could be taken as key texts in support of Calvinism.
JDS' retort has nothing to do with his shoddy hermeneutics; it's just a sudden change of subject intended to bias people against me, in essence: "That RansomOttawa is a Calvinist, and you know what they're like."
Point out how the poisoining the well fallacy works in the given argument, and note that it is actually an ad hominem fallacy: the debater has changed the subject from his opponent's arguments, to his opponent's character.