So klutzy that it obscures what should be its comic highlight: Caligula making his horse a consul. Too dull and repellent to be a guilty pleasure, this porno-epic cost $17 million, most of which went into Danilo Donati’s superb sets and the handful of stars who were persuaded to sign on. Embarrassing himself and nuking his career, Malcolm McDowell stars as Caligula, who at one point forces a couple to fornicate in front of him and then rams his fist up the man’s ass. Other actors like John Gielgud and Peter O’Toole manage to keep their dignity, if only because they’re killed off in the first hour. According to the credits, nobody wrote or directed the film — Tinto Brass only did “principal photography” (meaning he directed it, all right, but someone else messed with it, which we’ll get to in a minute); the movie is “adapted from an original screenplay by Gore Vidal,” who sued to take his name off the film. Vidal possibly shaped the script as an irreverent, no-holds-barred chronicle of Caligula, one of the Roman Empire’s looniest rulers, but producer Bob Guccione, the publisher of Penthouse, turned it into a Penthouse movie. Sprinkled among the lifeless talking-heads scenes are about six minutes of hardcore porn footage shot in gauzy soft focus against white backgrounds or under muddy red-brown lights. A catalog of sexual kinks (oral, anal, a woman bathing in semen), Caligula is also repulsively violent (castrations, disembowellings, and a gigantic rolling machine whose blades behead people buried up to their necks in the center of the coliseum). Yet none of it has any heat. The men and women copulating for posterity have one eye on the paycheck — they’re just porno background. Caligula is both sleazy and boring, an unforgivable combination. There is an uncut version (156 minutes) and an R-rated version (102 minutes); the longest known cut runs three and a half hours!