A trio of footloose bridesmaids, out on the town on the eve of the wedding, with mischief on their minds -- sounds like the setup for three coins in a fountain of fun. But as it goes with most such events, the shenanigans don't live up to expectations.

Kirsten Dunst, Lizzy Caplan and Isla Fisher are Regan, Gena and Katie, 30-ish pals who were known as "the B-Faces" in high school. They reunite for the nuptials of their nicer, fatter friend Becky (Rebel Wilson, the weirdo roommate of "Bridesmaids"), whom they used to call "Pigface" behind her back.

In the beginning, the action skips along like the first 20 minutes of happy hour. Cocaine is consumed, the bride is insulted, the bridal gown is ripped and stained during some drunken horsing around, sending the hormonal hellions off on a mission. But by the time the wee hours roll around, the minutes drag like they do when you're the only one who wants to leave the party.

One problem is a boringly predictable coupling up of the bridesmaids with the cardboard groomsmen. Even Adam Scott ("Parks and Recreation"), master of the hilarious straight face, falls flat. The chemistry between Caplan and Scott, old high-school flames, is nowhere near as charmingly fake-antagonistic as it was when they played caterers attracted to each other in the short-lived cable series "Party Down."

As the ditzy dimwit for whom poor judgment is a way of life, Fisher provides most of the LOL. Caplan brings a dour adorability to world-weary Gena. Dunst, who as bossy, snippy Regan is the Alpha B-Face, is in control -- except when, like, she's having meaningless sex in a strip-club bathroom.

Written and directed by Leslye Headland, "Bachelorette" is based on her play of the same name, which was a big off-Broadway hit in 2010. The film version could have used the confines of the stage to sharpen a promising premise that dissipates into dead ends on screen.

The dialogue, often too loosey-goosey improv to elicit laughs that some tightening could have prompted, does have its golden moments. "You had an abortion without me?" Katie whines to Gena. Cringe-worthy, yes, but it works because underneath the dark absurdity is the poign- ant tug of all-for-one friendship.

Most of the film's one-liners, however, will only amuse those as high as these stumblebums are -- "Why are doors so heavy?" "She really goes from 60 to zero."

"Bachelorette" has been available via video on demand for nearly a month, doing very well despite reviews bemoaning the characters' unlikability. Some of that criticism smacks of slut shaming, as if single girls on a hedonistic bender is an irredeemable scenario. In the 21st century, women can use vulgarity, vomit and idiocy to as much comic effect as the guys of "The Hangover," as "Bridesmaids" demonstrated last year. And who cares if no lessons seem to be learned? In a raunchfest like this, we expect our protagonists to be narcissistic, vapid, immature, even unlikable.

Redemption isn't an issue. "Bachelorette" commits only one crime, but it's a make-or-break offense -- it's just not quite funny enough.

Kristin Tillotson • 612-673-7046 Follow her on Twitter: @StribKristin