Its comic apex is a monologue about the finer points of giving oral sex delivered by Gena to a stranger sitting next to her on the plane from Los Angeles to New York. Ms. Caplan’s portrayal of this smart, self-loathing woman who conceals her vulnerability under a toxic, too hip veneer of sarcasm evokes the combative attitude of Janeane Garofalo, minus the political edge.

Hours before the nuptials, the three women’s bad karma catches up with them when Becky’s wedding gown is dragged out of a closet and accidentally torn while Regan and Katie cram themselves into it for a Facebook photo. By the end of the movie, the garment has endured more wear and tear than most dresses in a year. Most of the remaining story is a frantic wild goose chase — with detours — to repair and clean the gown, which has been stained by a cocaine-induced nosebleed.

The movie’s race around Manhattan is a good excuse to give “Bachelorette” some air, along with a screwball energy lacking in the play, which was set entirely in one room. When not looking for a dry cleaner or a seamstress, Regan and her pals crash Dale’s bachelor party and follow him and his groomsmen to a strip club, all the time guzzling and snorting their brains out.

Regan hooks up with her cold, handsome male equivalent, Trevor (James Marsden), in the club bathroom while yapping on a cellphone. Katie passes out while being pursued by Joe (Kyle Bornheimer), a slavishly adoring high school classmate whom she doesn’t remember until he reminds her that he sold her pot. This very pretty airhead is always at her wits’ end.

“I don’t know what to do with someone I really like except sleep with them or get really drunk,” she frets.

Gena’s old boyfriend Clyde (Adam Scott) shows up as a member of the groom’s party, and as these exes warily revisit their troubled history, the movie reveals signs that it has a heart. At the core of the film is Regan’s arrogant Little Miss Fixit, who in a confessional moment peevishly complains: “I did everything right. I went to college. I exercise. I eat like a normal person. I’ve got a boyfriend in med school, and nothing is happening to me.”