Jennifer Lawrence doesn't use social media very often, so when she does, you know it's got to be about something important. The 24-year-old actress posted a message to Facebook on Friday in an effort to clear up the rumor that she and director David O. Russell had a heated argument on the set of their new movie, "Joy." TMZ first reported the alleged "showdown," claiming Lawrence and Russell got into a "loud argument" on Tuesday in Boston while filming a scene.