This week's short fallacy is simply "distracting with an irrelevancy", and it's called the Red Herring.
Something Smells Fishy
How often are you talking with someone about one thing, then they bring up something else under the guise of the current discussion, and suddenly the conversation has shifted to their topic? This is an example of a red herring fallacy, a logical error that you may have heard of, if not only in name, which comes from the sport of fox hunting. Strong-smelling smoked herrings are used to throw off the scent of the fox and lead its pursuers down a different path.
The essence of this practice translates to logical argument: if your opponent brings up an irrelevant point and you follow it, then you've just been duped by his red herring. This fallacy of irrelevance may also be found in conjunction with the Straw Man fallacy. The two diversionary tactics snag the interest of a debater and can lead off in a completely different direction. Be wary of a smoke-screen argument that makes you say, "That's beside the point..."
An example of a red herring is this notion of "absolute knowledge". Proselytizers will usually say something like "How you do know there is no faeries/leprechauns/God? You'd have to know everything about everything, etc." No one can have absolute knowledge about anything, and it's a distraction to chase that trail. To the extent that we can know of these things, we can reasonably say "There is no faeries/leprechauns/God".