Since your definition of clear and private thought might be circular, perhaps it is not the unclarity of the pomos you have a problem with but your assumptions about what constitutes, in some way, rational and private thinking.
Many pomos will have a problem with any definition you will devise, however, pointing to the obvious absurdity of disengaging one's thought from context to be able to provide either universal definition of vagueness or thought or even private thought.
I imagine there will be many pomos who would attack the entire notion of private thought as ultimately meaningless. I do not think so, although much hinges on what you mean by private versus public thought and how that relates to language.
As it is, I find the fastidiousness of a Derrida, say, in elaborating his argument, and the painstaking effort he makes at looking at every facet of an argument's meaning as indicative not of vague thought as much as extreme clarity.
The problem is, I think, most people who think as you do, assume that clarity of thought relates to systematic propositions and analysis that conform to an ability to represent things objectively. But this latter is exactly what the deconstructionists question. They are willing to forego an objective framework in which life in its diversity becomes mesmerized, and seeks to allow things to stand clearly in all their interconnectedness. This interconnectedness is often messy and vague. But the attempt to clear up the messiness only begins to deprive things or individuals of their particularity.
Truth is subjective, as Kierkegaard said, and as some pomos take great pains to tease out of reality; instead of simply generating syllogisms that prove what is already assumed. Pomos eschew imposing pre-conceived notions of what constitutes objective truth onto the manifold diversity of human life. They attempt to recapture the meaning that originates in one's active relationship with and to the world, not some Cartesian notion of consciousness divested of context.
> Until I decided that "pomo" was so vague as to not be even usable in
> private thought, I had always classified objections to Meta-Narrative
> as "postmodern." In any case the first time I ever heard anyone reject
> a point because it was a "narrative" (the occasion was in an Eng. Dept.
> discussion forum at ISU) the only response I could give was to drop
> my jaw. I would assume that while meta-narrative and thinking are
> not quite synonymous they are so closely intertwined that to reject
> one is to reject the other.