Jean-Francois Lyotard: postmodernism is..."incredulity towards all grand narratives."
Yes, it's as simple as that. I believe that trying to encapsulate postmodernism that easily is absurd - because it's really a blanket statement for a movement that includes deconstructionism, existentialism, French phenomenology, linguistics, semiotics, and philosophy. It's not pseudo-philosophical, it's supra-philosopical. Or, as my entire class stated again and again when we did speeches on the damn thing: "Postmodernism's really hard to define."
If you treat postmodernism as a destructive force ONLY, you'll get along just fine. Just don't try and see what it puts in place of modernism. Besides, I fundamentally don't believe that postmodernism is a 'rejection of modernism' - I think it's simply a refutation of belief in an absolute. It's like Umberto Eco said (all you 2005 pomo kids take note - good quote coming up) "I have come to view the whole world as an enigma; a harmless enigma that has been made terrible only by our own mad attempt to interpret it as though it had an underlying truth."
Perhaps in our fragmented, discursively-pluralistic world, postmodernism is simply a more accurate depiction of the true state of events.