How To Debate A Post-Modernist this is more of a historical period — Moliere
According to Chomsky it was around the 1970s when a group of Parisian intellectuals and maoists (e.g. Julia Kristeva & Co.) could no longer deny the atrocities in Asia for which other maoists had been responsible. So, did they reconsider? No, instead they became outspoken post-structuralists who rejected the self-sufficiency of right, wrong, true, false, good, bad and so on. As I understand it they exploited problems of philosophy as a means to get away with a dubious past.
Not all Parisian intellectuals were maoists, of course. But most of them had (or still have) an obfuscatory style of writing which has the illegitimate benefits of making themselves (or their interpreters) the sole intellectual authorities of their claims, and thereby also immune to criticism. If one does not blindly accept their claims one runs the risk of being intimidated and accused for being ignorant.
I think postmodernism has little to do with philosophy, although demarcation seems to be a recurring theme. Kristeva, Derrida, Baudrillard, Foucault, Deleuze etc. became intellectual rock-stars by making all kinds of outrageous claims embedded in impenetrable jargon which attracted the intellectually curious as well as those with a grudge against established knowledge, skills, or habits.
It is not over yet, though. Currently many professors at our universities are old fans of these rockstars. Most graduates from my school of architecture know very little about how to build, because many of their teachers think it is naive to believe that there would be right or wrong ways to build. As if an absence of right and wrong would make us creative. But the way we build will therefore be determined by power instead of knowledge or rightness. I don't think that's so creative.