What were directors Ben Affleck and David Fincher discussing when they had lunch in Brentwood, Calif., on Tuesday afternoon? We don’t know. But here’s hoping it’s a collaboration, and that it will be filmed in Ben’s hometown. Fincher has already worked locally; he filmed part of “The Social Network” in Cambridge. . . . Meanwhile, “R.I.P.D.,” which was filmed here, is about to hit theaters. Before it does, stars Jeff Bridges and Ryan Reynolds are coming to town for a special screening Sunday with some of the first responders to the Marathon bombings, including Boston police and fire, EMTs, MIT police, Watertown police, and volunteers from the Marathon medical tent.