Actor turned writer/director Peter Berg says his mantra during the making of "Very Bad Things" was "Death before boredom." It shows. Extremely gruesome and packed with violence, "Very Bad Things" is most certainly not boring. The film has a relentless forward thrust, an energy that keeps the proceedings as involving as they are bloody, until it runs out of gas near the end. The film has too much of a conscience to fully succeed as a black comedy and is too farcical to fully succeed as a straightforward horror film, but damn if it isn't perversely entertaining most of the way along.

The Tarantino-influenced black comedy, about a bachelor party gone horribly wrong, desperately wants to be a boy's club version of "Heathers, " but doesn't know how to get there. Berg hops all over the place, from humorous nihilism to blunt-edged social commentary. His finished product plays essentially as a messy curiosity, albeit a fascinating one.

It begins with a trip to Las Vegas. Kyle Fisher (Jon Favreau) is days away from marrying Laura (Cameron Diaz), a young woman obsessed with creating the perfect wedding ceremony. Determined to satisfy his fiancée, he continues working on wedding arrangements by car phone, even as his buddies urge him to relax and enjoy the ride to Las Vegas for his bachelor party.

Kyle's pal Robert (Christian Slater), a real estate agent and motivational book zealot, has assembled everything necessary for a night of gambling and debauchery; from liquor and cocaine to a beautiful hooker. Joining in the revelry is family-man Adam (Daniel Stern), his tightly- wound brother, Michael (Jeremy Piven), and Charles (Leland Orser), an introspective cipher.

Things go swimmingly until Michael, during an over-enthusiastic session of stand-up sex, accidentally impales the prostitute on a bathroom coat hook. The shaken men debate what to do, with Robert arguing for a quick disposal of the body in the desert. He dismisses all legal and moral issues, coolly stating "this is just a 105 pound problem that has to be moved from point A to point B." With strong reservations, the others agreed to the plan, only to have matters further complicated when a security guard arrives and spots the corpse. Ever the problem-solver, Robert uses a corkscrew on the guard, removing the witness and doubling the body count.

The rest of the story follows the men on their damage control mission, with as many plot twists and turns as the aforementioned corkscrew. Each man reacts to the group decision in different ways, ranging from crushing guilt to gallows humor. Meanwhile, Laura continues her steamroller preparations for a wedding that will happen, no matter what.

With an actor at the helm, it's not surprising that the impressive cast of "Very Bad Things" is given considerable room to stretch. Christian Slater and Cameron Diaz have the juiciest parts, with Slater entertaining as a character who is essentially an older version of the sociopath he played in "Heathers." Diaz is a hoot as the marriage-at-all-costs bride to be. Her steely determination reminded me of Debbie Reynolds' ceremony- fixated character from "In and Out," only much more ruthless.

Jeremy Piven is excellent as Michael, imbuing him with a great manic energy. The character is an explosion waiting to happen and Piven, known for his intense portrayals, perfectly captures Michael's hair-trigger emotions. Daniel Stern is less successful as Michael's brother, Adam, delivering a performance as a borderline hysteric that rarely varies in tone (incidentally, with all due respect to the intricacies of genetic coding, there is no way in hell those two guys could be brothers). As Charles, the sketchiest of the men, Leland Orser projects a jittery quality that keeps his character interesting.

Which brings us to the groom. Jon Favreau, who scored a hat trick with "Swingers," is an extremely appealing actor, but oddly bland here. Kyle would have been more effective had Favreau cut back on the mealy-mouth squishiness and given the guy a little more oomph. Of course, all of the actors faced a challenge with their roles. After all, how do you play characters who are supposed to be tragic, despicable and funny all at the same time?

There are some big laughs in "Very Bad Things," although not as many as there could have been. Berg can't decide whether he's making a full-out tasteless farce or a noirish horror story involving real feelings, and refuses to commit to either. The potential impact is muted by the film's constant shifts in tone. One moment we're watching a character break down in heartfelt grief and shame over his actions, the next moment we're listening to one-liners about dismembered bodies. Berg punches so many contrasting emotional buttons that the whole system finally short circuits. The film's closing shot, intended to either provoke reflection or provide one last sick laugh, drew no response whatsoever from me. By that point, I just wanted to go home.