Faced with the task of following the runaway success of There's Something About Mary, Peter and Bobby Farrelly have come up with a seemingly foolproof concept for their fourth film, a Nutty Professor-style slapstick vehicle for their Dumb And Dumber leading man, Jim Carrey. In a role that plays on his strengths as both a physical comedian and a relatively controlled thespian, Carrey here plays a good-natured Rhode Island state trooper who becomes a doormat after his wife leaves him for a brilliant dwarf. Abused by nearly everyone in his small town, Carrey's repressed rage soon surfaces in the form of a sadistic second personality, a hyper-confident creep who speaks in a Clint Eastwood rasp and enacts amusingly over-the-top revenge on his flippant tormentors. Renée Zellweger co-stars as Carrey's love interest, a street-smart looker on the lam from a sinister ex-boyfriend and a cadre of crooked cops. It's a promising set-up, and at its best, Me, Myself & Irene pulls off some ingeniously constructed physical comedy. After a knockout opening, however, it becomes a prisoner to its perfunctory plot, a development that dooms its comic momentum. In great comedies, plot and exposition never detract from the comedy or call attention to themselves. In Me, Myself & Irene, the laughably cliched "thriller" elements seem drawn from a different, inferior movie. While uneven throughout, the film really loses it in its final third, beginning with a Jim Carrey-beating-himself-up scene that cannibalizes an almost identical one in Liar Liar and sets the tone for a half hour of unsuccessful physical comedy tethered to an excruciating chase scene. Like There's Something About Mary, Me, Myself & Irene has a disarming sweetness that almost pulls it through its many rough spots. As one-third of a great comedy, however, it's a disappointment, a sporadically brilliant mess that never makes good on the promise of its hilarious start.