Sleaze merchant Bob Guccione, the Penthouse publisher who died yesterday, once tried to buy credibility by financing a historical film about debauched Roman emperor Caligula, assembling a script by Gore Vidal and a cast including John Gielgud, Malcolm McDowell, Helen Mirren, and Peter O’Toole. Parsing the notorious movie to guess which bits were shot under the original auspices of making a “real” film, it’s clear the project went off the rails pretty quickly, because even the straight dramatic scenes involving the principal actors are overwrought in terms of florid dialogue, undisciplined performances, and wall-to-wall ugliness. The bit in which a man’s penis is sliced off and fed to a dog is exactly as enjoyable as the scene of Caligula (McDowell) raping a Roman citizen’s virginal bride. (An equal-opportunity violator, Caligula also services the groom. With his fist.) To make matters so much worse, Guccione decided after director Tinto Brass wrapped principal photography that Caligula wasn’t rough enough, so he recruited a cast of dwarves, grotesques, studs, and Penthouse Pets to shoot reel after reel of hardcore sex that was then intercut (often randomly) with the dramatic scenes. Vidal tried to get his name taken off the picture, and the leading actors were mortified that they couldn’t be removed from the monstrosity entirely. Genuinely vile from its first frame to its last, Caligula is morbidly fascinating as the most pornographic film ever made with name actors, but it’s about as fun as dentistry without anesthesia. FYI, there’s an R-rated version of the picture available on DVD, but what’s the point of that? The only reason to slog through this atrocity is to see how far Guccione really went when carving out his loathsome little niche of cinema history.