Eugene Volokh has a great post up (and Matt Yglesias some interesting commentary) on a longstanding pet peeve of mine: the indiscriminate conservative use of "moral relativist" as a term of abuse against liberals and libertarians. (The preferred Straussian variant is "nihilist.") In my experience, most such uses are, as Volokh suggests, pretty confused.
But what's really annoying is when the transparent speciousness of the charge is then used to derive a witless "gotcha" charge of contradiction. So, for instance, I can't count the number of times I've seen some keyboard jockey post the equivalent of the following to some message board: "You know, you think we should be tolerant of all sorts of sexual deviants, anything goes—but you're not so tolerant when you call us bigots for wanting to exclude those people." A few clicks of the mental gears, of course, would make it obvious that the underlying position wasn't: "all judgements about sexual ethics are equally valid" but rather "the right view of sexual ethics entails that there's nothing wrong with practice X."
I assume what's going on there is that some folks are so hopelessly Manichean that they can only imagine the dispute being Morality (theirs) vs. amorality, rather than between distinct moral theories—think 12th century Englishman asking a Buddhist whether he worships God or the devil.