That's called devil's advocate trolling, or Poeing (named for computer scientist Nathan Poe, who famously said that without some kind of indication, it's almost impossible to tell if an extremist online is joking or serious).
Yes, I've done it. I used to do it anonymously on Yahoo! Answers, to make argumentative Christian creationists realize how ridiculous they sounded. I even went as far as to make an account called Nathan, with a profile picture of Edgar Allan Poe, just to test Poe's Law to the extreme. At first, people thought I was serious. Then I started adding more and more quotations from Edgar Allan Poe into my posts, until people finally got the joke. It actually took a couple of months.
