Not all girls are sugar and spice everything nice.  Some are bitter and mean and sometimes that behavior can be downright hilarious.  For its first two-thirds, Bachelorette is unapologetic in how ugly, filthy, dark, and angry it's willing to be for the sake of a laugh.  The three main characters are sad and despicable, and writer-director Leslye Headland has no reservations about trying to justify her characters behavior until the last act.  Then the movie falls into a sappy place where the humor drains away and we're asked to root characters who were hilarious but completely beyond redemption.

Regan (Kirsten Dunst), Gena (Lizzy Caplan), and Katie (Isla Fisher) are surprised and seriously annoyed when their fat friend Becky (Rebel Wilson) becomes the first of their group to get married.  When they're not busy being total jerks, the three bridesmaids are being petty about their own baggage.   Regan expected to be married first, Gena is holding a grudge against her high-school boyfriend Clyde (Adam Scott), and Katie is realizing that she may be too stupid to live.  The night before the wedding, the drunk and coked-up gals, in an act of ultimate bitchiness, try to fit into Becky's massive wedding dress and end up ripping it.  The three then go on a mad dash to try and fix the dress, which leads them on various misadventures.

For about an hour, Bachelorette does a terrific job of mixing up its humor.  Regan is venomous and short-tempered, Gena is foul-mouthed and devil-may-care, and Katie is a bimbo who is unaware of how insensitive she can be.  Caplan and especially Fisher are brilliant in their comic delivery and timing.  Caplan brings a dry humor to her vulgar dialogue (she kills in a scene where she's talking to a stranger about how much effort women put into blowjobs) and Fisher perfectly blends the sweet, ditzy, and slightly mean aspects of her character.  Unfortunately, Dunst is stuck as the straight-woman and doesn't get to deliver as many jokes as her co-stars.

But everything we loved to hate about these characters fades away as the movie softens up in the third act.  Caplan and Scott carry over their Party Down chemistry (although I'm convinced that Scott could play well off anyone), but I don't care about the characters' past relationship.  I don't care if they fall in love again.  And if it does happen, it shouldn't be done in such a sweet manner.  We also learn that Regan and Katie have their own separate issues and it's as if Headland wanted to say, "I know these characters were horrible, but they also have a sadder side.  That makes them real people now."  Adding a sob story does not make them real people now, and it strips the movie of its tone and most of its humor.

It's okay to be a total bitch as long as you're hilarious and don't make excuses.  For the majority of its runtime, Bachelorette and its actresses embrace their bitchiness.  The movie relishes the mean jokes, the raunchy humor, and the unashamed drug use.  This isn't a Jane Austen novel, and people are going to be shocked by the filthiness of the jokes, not that the jokes are being made by women.  The guys in The Hangover didn't need excuses for their personalities.  Why should the ladies of Bachelorette be any different?  Mean-spirited comedy doesn't give a shit about your genitals.

Rating: B-

For all of our coverage of the 2012 Sundance Film Festival, click here.  Also, here are links to all of my Sundance reviews so far: