The most basic rule of a screen romance is that you have to root for the couple to become a couple. And that just kills “Something Borrowed.” The winsome, girl-next-door charms of Ginnifer Goodwin and the witty way with a one-liner of John Krasinski can’t overcome chemistry-free casting and a flawed premise.

Can we root for a woman to steal her best friend’s fiancé?

And what a fiancé. Colin Egglesfield, as the law school crush who is about to marry that best friend (Kate Hudson), is a Tom Cruise clone without the teeth and without the sparkle. Whatever his gifts as an actor, he doesn’t have anybody at hello here.

“Borrowed,” boringly boiled down from Emily Giffin’s conflicting points-of-view novel, is “Gone With the Wind” where Scarlet wants, gets and is perfectly content with that wuss Ashley Wilkes.

Goodwin, charmingly lovesick in everything from “He’s Just Not That Into You” to “Ramona and Beezus,” plays Rachel, a lawyer who turns 30 as we meet her, and sits back and lets her vivacious, brassy and self-centered pal Darcy (Kate Hudson, making a habit of this sort of role) hijack her birthday party.

“I don’t get how you let her win all the time,” Rachel’s guy pal Ethan (Krasinski) complains. He points to Darcy, dancing on the bar and jokes, “Whoa. Center of attention? That’s weird.”

Rachel the not-quite-wallflower always does what Darcy wants, and what Darcy wants is Rachel to be her maid of honor. But on the night of that party, Rachel and Darcy’s intended, Dex (Egglesfield) have their true confessions moment. Each hid a crush from the other in law school. And when Darcy elbowed her way in, Rachel just stepped aside. Now she has regrets.

After a night of sex with Dex, she has more of them.

The rest of the movie is Rachel trying to reconcile her actions and her desires for Dex with Dex’s refusal to stop the wedding train before it reaches the station. Both women are attracted to his gallantry. But when it comes to telling Darcy or his parents, either at dinner or at the many weekends they arrange to get the whole gang together in The Hamptons, Dex is Mr. No Guts, willing to just do “what I’m expected to do.”

Others in their orbit include the hipster-womanizer Marcus (Steve Howey, generic in a generic role) and Claire (Ashley Williams), a needy woman Ethan once slept with and spends all his time fending off.

Thank heavens Krasinski, at least, had the screenwriter’s ear. He makes every one-liner land. “The Hamptons are like a zombie movie directed by Ralph Lauren.”

Director Luke Greenfield (“The Girl Next Door,” “The Animal”) lets everybody else come off flat and dull, even the accomplished Goodwin. Hudson does her best to make Darcy hateful, but never manages to be more than mildly annoying. We all have friends who suck all the oxygen out of a room. We don’t cheat with their fiancés.

And the message of it all may be the blandest, most trite ingredient on the screen here, that “Sometimes good people do bad things.” Talk about “Something Borrowed.”

MPAA rating: PG-13 for sexual content including dialogue, and some drug material

Cast: Ginnifer Goodwin (Rachel), Kate Hudson (Darcy), Colin Egglesfield (Dex), John Krasinski (Ethan)

Credits: Directed by Luke Greenfield, written by Jennie Snyder, based on an Emily Giffin novel, produced by Broderick Johnson, Molly Smith, Aaron Lubin, Pamela Schein Murphy, Andrew Kosove and Hilary Swank. A Warner Brothers release. Running time: 1:54