Revealing character. The two major ways we do it is through dialogue, and through action. Or sometimes both: There are million discussions to be had about THE DARK KNIGHT, but one of my favorite moments was the second time The Joker told the story of how he got his scars. And it was a different story than the first...so in that one moment you realize that not only is the Joker lying, but that he lied the first time too. Suddenly you can't really trust anything that comes out of his mouth. And it's been shown to us, rather than told.
For the record, there may be an inflated amount of hype about Heath Ledger, but I still thought his performance was spectacular.
For an entirely different record, a coworker of mine has taken to grabbing his crotch a la Michael Jackson and yelling, "BLOG THIS!"
I guess that's dialogue and action too?