Southland Tales, that gonzo apocalypse job we gabbed about last week, premiered Friday at the ArcLight. Sarah Michelle Gellar was dressed so the opposite of the potty-mouthed porn star she portrays, all demure in a neutral dress and long, conservative coat. Crap. At the Airborne-sponsored after-do, she hung in a VIP section with her old Buffy castmate Michelle Trachtenberg and new pro-mate Dwayne Johnson. But the former small-screen queen was suddenly press shy at said soiree, opting not to gab to any reporters milling round. Was she scared we were going to ask if refuses to do backdoor in real life, like her character in the movie, or somethin'?