Aporias, in televisual as much as in written texts, indicate points of knowledge which the consumer may reasonably be expected to share. When Sam and Dean encounter Little Red Riding Hood (Bedtime Stories, 3x05), they don't need to spend much time recounting the story's plot in detail. The audience, it is presumed, already possesses that information.
But what of the opposite extreme? When a text provides information not just once, but repeatedly, clearly its author has decided that the audience does not possess, but requires, that information. In the case of a weekly television series, repetition of basic information may be presumed to be for the benefit of the casual viewer who cannot be expected to "already know" the show's basic established canon.
The established viewer, who may see details of character or setting restated dozens or hundreds of times, can react to this repetition passively, accepting it as a necessary construct of the show. Paradoxically, however, these repetitions of basic canonical foundations may instead provoke an active resistant reading.
So it is with Dean's sexuality. Time and again Dean's heteronormative, enthusiastic (even predatory) sexuality is reestablished. Show after show points up this "necessary information." Quite probably most or even all new viewers absorb and accept that Dean is fully heterosexual, flirtatious, and sexually rapacious. Yet to the active, more invested viewer, the constant iterations raise questions. The requirements of serialized television create an artifact of doubt and suggest reinterpretations. Why, the regular viewer asks, does this need to be said so loudly and so often? If Dean's sexuality can never be presumed, can never achieve the certainty of an aporia, then space for reinterpretation opens up.
Nowhere is this reinterpretation more brilliantly yet logically displayed then in "pre-series" fics which deconstruct Dean's sexuality to equip him with past behaviors--and by extension, current desires--quite other than the driven heterosexuality the show insists on. "Don't Say You're Sorry" is a recent example (part of a larger "Don't" series, the first installment of which is also linked above). phantisma answers the question of how a young Dean and Sam might have survived, while at the same time posing and answering questions about Dean's sexual history--questions that, paradoxically, stem from canon's insistence on circumscribing Dean's sexuality. The resultant fic is not merely arousing, but convincing.
The lyrical and widely acclaimed "You Tasted All My Purity" is a second example of this questioning of canon's refusal to let Dean's sexuality become background, and of resistance to this overstatement and exploration of the doubts it raises. Coolly taking the opposite position--that Dean has not only had heterosexual sex, that Dean is not the two-dimensional sexual stereotype canon seeks to reduce him to--conquest ties Dean's masculine, and initially paternal, feelings towards Sam to an active use of his sexuality that is anything but the stereotypical "masculinity" the series-as-text proclaims.