You could, if you wanted, sit in a dark theater and simply check off the similarities between the blockbuster “Bridesmaids” and this fall’s “Bridesmaids” knockoff, titled “Bachelorette.”

Female bodily function jokes? Check. Inappropriate come-ons on an airline flight? Check. Crass, crude and fearlessly frank talk about sex, once reserved for the fraternity house? Check. Wedding dress disasters? Check-eroonie.

“My So-Called Life” and “Fast Ties at Ridgemont High” references, singing along with the over-used “I’m Gonna Be 500 Miles”? Uh, no.

Enthusiastic cocaine snorting, Xanax and alcohol abuse, abortion jokes … wait, say what?

Writer-director Leslye Headland aimed for “Bachelorette” to out-Bridesmaid “Bridesmaids.” She’s taken an equally accomplished cast (and a better-looking one) and hurled them at the same heartbreak, fiascoes and emotionally overwrought pathos of an impending wedding, filled their dialogue with F-bombs and amped up their behavior on coke — not the diet kind either.

And what she’s given us is an “Oh no they DIDN’T” romp that never quite romps, a teary-eyed string of taking-stock moments without tears, and a pretty serious squandering of major-league movie talent.

The four “B-Faces” have reunited because one of their number is winning that race to the altar, 13 years after graduation

Kirsten Dunst is icy, cool and bitter as Regan, the 30-something, hyper-organized professional woman, at a loss as to why she hasn’t been the first in her quartet of high school pals to marry. That the dizzy, loose Katie (Isla Fisher) is still single, THAT she understands. Gena (a fierce Lizzy Caplan) has been living a drug-and-booze fueled nightmare since a romantic high school trauma.

And Rebel Wilson, of “Bridesmaids,” is to be the bride. One of the real rewards of the film is figuring out, eventually, what connected her to the others, how the plump girl nicknamed “Pig Face” got to hang with the hotties.

Regan is in the home stretch of snapping at one and all, organizing this fete as the maid of honor. But over a tiny window of time the weekend of the wedding we get to see much of her good work come undone.

It’s part reunion movie, part wedding disaster, and both parts are filled with bridesmaids behaving badly.

A guy flirts with Katie, who doesn’t remember him from way back when.

“We were in French class together.”

“I took French?”

An overdose warrants this exchange:

“Shouldn’t we get an ambulance?”

“No. She does this every weekend.”

And so on.

That’s what Headland goes for — cheap, broad shocks. And even if the situations are mostly recycled, the words can jolt a laugh out of you. It’s a well-cast film, with Dunst playing against her natural earthy warmth, Fisher (“Confessions of a Shopaholic”) doing the loose-and-dumb thing well. But Caplan (“127 Hours”) is the real breakout here. She lets us see the impulsive mood swings of an addict and manages to keep Gena likable and every bit as fierce as Regan, even as her ex-beau (Adam Scott) tells her “It’s not cute anymore.”

James Marsden is also cast against type as the player/ best man, a heel with a certain in-your-face charm.

It’s another movie aiming to show women who are “Hangover” crude, with a hint of wedding wish-fulfillment fantasy. The transitions from silly to “serious” don’t work. At all. We don’t invest in anybody, so there’s no mourning for the picked-on bride, the wedding or wedding dress that these self-absorbed brats are ruining.

So “Bachelorette” is like the abortive bachelorette party the film trots out — complete with stripper — a scene cut short in order to flip our expectations. It’s a tease for a movie the filmmaker couldn’t deliver.