One of the reasons that radical relativism (the idea that all "truth" is always relative) is false is that it is self refuting. All truth is relative … except, of course, the truth statement that all truth is relative! If all truth were relative, the sentence "There is no truth." could equally mean "I like cabbage." or "Excuse me sir, do you know the way to Timbuktu?" The comic above is humorous because the boy blatantly changes the rules of the game after the fact. But if radical relativism is true, concepts like fairness, guilt, tolerance, altruism, and shame become meaningless.

Although Greg Koukl and others do a fine job of refuting radical relativism, I don't see this as being a popular philosophy. It's just so ridiculous (on both philosophical and intuitive levels) that it seems unlikely that anyone would seriously hold this view (outside of insane asylums and graduate philosophy departments) and even if they did, that after careful scrutiny they would be forced to admit that they do not live consistently with their view.

Am I wrong? Is this a serious view of truth?

It seems to me the real problem is not relativism, or even postmodernism per se, but instead a particular type of intellectual laziness that can sometimes masquerade as "postmodernism". IMHO people don't gravitate towards relativism because they honestly think it's a valid way of looking at the world; they gravitate toward it because it absolves them of the responsibility to have to think about difficult issues. It's the equivalent of clasping your hands over your ears and going "lah-lah-lah-lah-lah". Of course, Christians can sometimes be guilty of the very same thing, but at least one thing that the atheist and Christian worldviews share is that one or the other, not both, of these worldviews is true, really true.