Rorty's liberal ironist embodies two distinct themes in Rorty's writing: the virtues of
liberalism (of which he is an unashamed apologist), and
postmodern irony.
Liberals, in Rorty's view (and borrowing Judith Shklar's words) are those who think that cruelty is the worst thing we do. A liberal hopes for nothing more, ultimately, than that suffering will be diminished, through whatever means we have or will develop.
An ironist is someone who faces up to the contingency of her own beliefs, and holds them unflinchingly anyway - "someone sufficiently historicist and nominalist to have abandoned the idea that (her) central beliefs and desires reach back to something beyond the reach of time and chance."1 An ironist has no illusions about her metaphysical grounding.
A liberal ironist, then, is a figure who acknowledges that her moral pretensions are dependent upon her time and place, and doesn't let that apparent relativism stop her from the philosophical or moral security that allows her to act on her liberal convictions, or to develop them.
1 Rorty, Richard: Contingency, irony, and solidarity (New York, Cambridge University Press, 1989) p. xv.