Nobody can do Christian outreach in a western university setting for long (especially in a liberal arts faculty) without encountering the argument that truth is relative and that absolutes are unknowble. And therefore the Bible doesn't reveal God because texts don't communicate meaning.

It is comparatively common in the academy to hear relativists (among whom all deconstructionists are counted) claim that their arguments and tenets are not refutable by someone who believes in absolutes. We are simply speaking different, mutually incomprehensible, languages, it is claimed. Which can be little more than a sophisticated way of saying we don't even want to talk to anyone who might challenge what we think.

here is the best,simplest arguement against someone who really holds that:

take any defining statement of relativism and apply it to itself and it doesn't work on its own terms

No "absolutist arguments" need to be applied. To give a basic (and slightly crass) example, applying the oft repeated statement "all truth claims are relative" to itself leads to nonsense. There is no way to test it on its own terms and therefore no way to validate or invalidate it. And therefore no way to trust it any more than we would trust the opposite statement. It exists in a philosophical nonsense category where its own self-referential nature leaves it without meaning of even a relativist kind.

For a longer example of how to argue against relativism in a university setting see the following lunchbar talk on How Can We Believe in a God in a World Without Meaning