And if you want your film to withstand the test of time, don’t be tempted to include of-the-moment pop-culture crazes like, say, a flash mob.

“Friends with Benefits,” an otherwise springy rom-com, is saddled with two flash mob scenes, an unfortunate turn given how that phenomenon is already taking on the whiff of Macarena rot.

Then again, “Friends with Benefits” seems a bit infected with the sort of preciousness that leads throngs of people to sing and dance at shopping malls and wedding receptions. While the movie is certainly smart and playful, especially by contemporary rom-com standards, it also oozes with an eager-to-please swagger. Fast dialogue, kinetic edits and a wall-to-wall soundtrack smack of the filmmakers’ desperation to show off their hipster bona fides.

Like “No Strings Attached” from earlier this year, the picture takes the premise of romance blossoming from commitment-free sex. Justin Timberlake (“The Social Network”) is Dylan, a hotshot Los Angeles blogger who is lured to New York by corporate headhunter Jamie, played by Mila Kunis (“Black Swan”), for a dream job as GQ’s art director. The two quickly become fast friends and find they have some things in common. Both are attractive, lovably shallow and look great naked, albeit in a soft-R way.

More to the point, Dylan is “emotionally unavailable” and Jamie is “emotionally damaged,” and so they decide to meet each other’s sexual needs without the messiness of emotional attachment.

That arrangement turns out to be more complicated than they expect, of course, but director Will Gluck (“Easy A”) keeps things light and sexy, punctuated by witty dialogue from the Spencer Tracy-Katharine Hepburn playbook. There are also some very funny moments. The pair’s initial sex session is raucously good-natured. Dylan explains the unique challenge of peeing with an erection (“It’s like two lanes of traffic merging into one”) while Jamie offers a tutorial on how to pleasure a woman. Coupled with “Black Swan,” Kunis now has the distinction of two movies boasting memorable scenes of what might now be termed Kunis-lingus.

“Friends with Benefits” also has the advantage of two leads with onscreen chemistry and charisma to spare, factors that help compensate for their characters’ general vapidity. Gluck has assembled a fine supporting cast, too, with Woody Harrelson (“Zombieland”) as an über-macho gay sports editor and Richard Jenkins (“Hall Pass”) giving a customarily excellent performance as Dylan’s Alzheimer’s-afflicted father.

In the end, “Friends with Benefits” doesn’t flout the conventions of genre nearly as much as it would like to believe. To be sure, screenwriters Gluck, Keith Merryman and David A. Newman deserve credit for putting their romantic leads on equal footing without making a self-conscious deal of it. But the film’s winking digs at romcom cliché grow tiresome as things chug along to genre-ordained conclusions. Better than some, worse than others, “Friends with Benefits” ultimately plays it safe.

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