Gilly (Chris Klein) reacts to his "haircut" from Jo (Heather Graham) in Say It Isn't So

Chris Klein (American Pie) stars as Gilly Noble, a lonely animal control officer in Shelbyville, Indiana. Gilly was raised in an orphanage and never knew his real parents. He has a private eye named Vic Bloomfield (Brent Briscoe) looking for them, but nothing turns up. One day, Gilly meets a new-in-town hair stylist named Jo (Heather Graham). She actually gives lousy haircuts, but is so sexy that Shelbyville's men line up anyway. Gilly is equally smitten; he falls in love with Jo even after she accidentally stabs him in the face with scissors and cuts off the top of his ear. Before long, they have consummated their relationship. Her parents - Valdine (Sally Field) and Walter (Richard Jenkins) - aren't so wild about Gilly. They prefer Jo's ex-boyfriend Jack (Eddie Cibrian) who lives back in Beaver, Oregon.

Then Vic calls with startling news: Valdine is Gilly's mother. He and Jo are siblings. After puking in a toilet, Jo returns to Beaver, vowing to never again see Gilly. But Vic was wrong, a fact proven 16 months later when Valdine's real son, Leon (Jack Plotnick) locates her and shows up at the doorstep. Gilly heads for Oregon to tell Jo the news but she's already engaged to Jack. And since Jack is rich, Valdine and Walter want the marriage to go through. They fax a picture of Gilly to the Beaver police department, warning them that he is "a sexual predator." From that point on, Gilly's attempts to contact Jo are foiled by people who think he's a pervert trying to sleep with his sister again.

Say It Isn't So has a wonderfully naughty premise, perfect for this Jerry Springer age we live in. I'm not sure that incest is funny, but mistaken incest...maybe. You just know that this kind of thing has happened for real somewhere, so why not use it for comedy's sake?

As creepily funny as the premise is, the execution leaves something to be desired. What makes the Farrelly brothers' films work is that they are sweet underneath. There's Something About Mary and Me, Myself and Irene are love stories that just happen to be punctuated by grossout humor. Say It Isn't So starts out with the gross stuff and then tries to wedge in a love story. As proof, I offer a reminder that this is the film in which Gilly disguises himself by gluing someone's pubic hair to his face. And later, while repeatedly slapping a cow on the backside, he accidentally jams his arm up there. It was weirdly cute when Cameron Diaz rubbed Ben Stiller's semen in her hair; it's just icky to watch Gilly caress Jo's face knowing where that hand had been.

The humor is also surprisingly cruel in this movie, something the Farrellys never indulge in. Walter, for example, has suffered a stroke and talks though a voice box. The screenplay (by Peter Gaulke and Gerry Swallow) tries to mine laughs by having him repeatedly swear through the thing. He's also in a wheelchair and gets covered in pigeon feces and, later, bees. Another character is Dig (Orlando Jones), a hippie with two missing legs who helps Gilly in Beaver. Why is he missing his legs? Basically so the film can do cheap jokes about his prosthetics falling off. Mental patients, Pakistanis, and rednecks are also the victims of cruel barbs. (Well, okay...rednecks have it coming.)

Perhaps the biggest mistake of all is that the actors perform their scenes as though they think they are being funny. Big, big, big no-no in this kind of comedy. If you want to do this right, you have to play it absolutely straight. You can't wink at the camera or overplay your hand. There's Something About Mary (the film this one is most clearly modeled after) worked because they took the romance seriously. The wild humor snuggled in nicely once we cared about the characters and their relationship. In Say It Isn't So, the actors look so excited to be in a wacky Farrelly-esque comedy that they never breathe any life into their roles. They seem to believe that they can coast by on the gags.

There are a few laughs in the movie, a couple of them big. But Say It Isn't So is mostly a disappointment. It's too mean-spirited to ever make us care and too self-knowing to send us into comic ecstasy.

( out of four)

Say It Isn't So is rated R for strong sexual content, crude humor and language. The running time is 1 hour and 33 minutes.