Maggie's Farm

An argument ex silentio claims "You respond with silence, thus I am proven right."

From Wiki: 

"In general, the claim that the absence of something demonstrates the proof of a proposition. An argumentum ex silentio ('argument from silence') is an argument based on the assumption that someone's silence on a matter suggests ('proves' when a logical fallacy) that person's ignorance of the matter or their inability to counterargue validly."

Of course, there are many reasons for silence besides an inability to make a counterpoint, including a simple lack of interest in pursuing a line of discussion or, as I have often found myself doing in debates with Liberals, reverting to silence out of a feeling of futility.

In the blog world, the common expression "crickets chirping" is a cute way of implying an ex silentio argument. Sometimes it's right, sometimes an error.

Augean Stables has a pretty good example of this fallacy in a debate he is engaged in about the al Durah affair.