At its best, dark humor has the power to speak profound truths about the harsher aspects of life. Over the past few decades, however, the black comedy has witnessed a dispiriting race to the bottom, as shrill, misanthropic, shock-obsessed entries have engaged in an epic game of one-upmanship, with audiences serving as the ultimate victims. A pathetic wallow, first in misanthropy and later in sentimentality, How To Kill Your Neighbor's Dog stars Kenneth Branagh as a theatrical bad boy whose wife (Robin Wright Penn) is as kindly and upbeat as he is miserable and pessimistic. When not delivering endless self-satisfied monologues about such fresh topics as how hard it is to smoke in L.A., how stupid everyone is, and what the deal is with children, Branagh works on his new play with such classic caricatures as a swishy gay director (David Krumholtz) and a dim actor (Johnathon Schaech). Dog clearly views its protagonist as a cheeky font of Molière-worthy bon mots, but he's more like a bad comedian inexplicably convinced that he's the second coming of Oscar Wilde. After doling out glib misanthropy for 70 minutes, Dog takes a wildly implausible detour into sentimentality when Branagh bonds with a neighbor girl and transforms from a punch-worthy jerk into a big softie over the course of one magical montage sequence. He then alternates being an insufferable asshole in one scene and a kindly, paternal figure in the next. Meanwhile, a subplot involving Branagh's Alzheimer's-stricken mother-in-law (Lynn Redgrave) takes a film that's every bit as vapid as the culture it purports to satirize, and pushes it into new levels of exploitation.