“It is possible, after all, to 'fake' the 'realest' possible 'evidence' of heterosexuality: man or woman, one can participate in heterosexual marriage and even help produce a brood of spawn and still 'turn out' to have been 'living a lie,' to have been 'really' gay or lesbian all along. Precisely because there is no final 'proof' of heterosexuality, heterosexuality must constantly set about trying to prove itself, assert itself, insist on itself. Indeed, as Butler argues, heterosexuality as hegemonic institution is finally nothing more than its own repetitive self-insistence, nothing other than 'a constant and repeated effort to imitate its own idealizations' (Bodies 125). Or, as Janet E. Halley puts it in regard to legalistic constructions of heterosexuality, normative heterosexuality 'is a highly unstable, default characterization for people who have not marked themselves or been marked by other as homosexual.”

As Halley continues: 'The resulting class of heterosexuals is a default class, home to those who have not fallen out of it.'
Source: Straight with a Twist (2000), p. 28.