Some people don't know when they've taken a joke too far. Others don't know how to quit when they're ahead. Both would accurately describe the filmmaking Farrelly brothers.

With films like "Dumb & Dumber" and "Kingpin," the duo has spearheaded a new "growth industry" in Hollywood, the gross-out comedy genre. No joke is too crass or too lowbrow for these guys.

However, at times they've shown that they're capable of so much more, which is why "There's Something About Mary" is their most frustrating film to date.

There's an underlying sweetness in it that hasn't been seen in either of the Farrelly brother productions. But it's tempered with sickening and tasteless sight gags.

Still, the movie does feature a pair of appealing leads. Ben Stiller stars as Ted Stroehmann, a lovable loser who is still pining for too-good-to-be-true beauty Mary Jenson (Cameron Diaz) 13 years after a high school prom mishap.

Unable to get her out of his thoughts, Ted hires shady P.I. Pat Healy (Matt Dillon) to find her. And when he does, Pat is also bewitched by Mary. He lies to Ted about her appearance and tries to woo her by posing as a rich architect and philanthropist.

Eventually, Ted finds out the truth and heads to Florida in search of them both, only to discover he's one of several men who are obsessed with the still-stunning woman.

Throughout the first hour, the jokes fly at a furious pace. But after that, the film really runs out of steam.

Also, the Farrellys still don't know when to simply describe something verbally rather than show it graphically, a bad habit that leads them to include gags that are just plain nauseating.

That's not to say the film is a complete waste of time. As mentioned, Stiller and Diaz are both quite good. And there are some riotous cameos, especially the presence of alternative-rock guru Jonathan Richman, who serves as the film's musical narrator (shades of "Cat Ballou").

"There's Something About Mary" is rated R for vulgar sight gags, both scatological and sexual, profanity, slapstick violence, nudity (some involving prosthetics), and use of a couple of ethnic slurs.