The philosophy is all about subverting epistemic certainty and rejecting the very concept of objectivity. Moral relativism isn't unique to Postmodernism, but it's a critical underpinning. As is the idea to reject objective truth.
You're arguing that I do not know what I'm talking about, except this was actually my field of study. I am very familiar with all aspects of Postmodernism and as I said before if you ask the Postmodernists they would agree with my assessment, although I'm sure they'd have more positive things to say than I do.