Just how many times can Natalie Portman and Ashton Kutcher have sex?

Let's put it this way. These pretty stars make a herd of randy rabbits look tired in Ivan Reitman's new comedy, "No Strings Attached."

They do it in parking lots. They do it in café bathrooms and hospital supply rooms, with Elvis Presley's peppy "Bossa Nova, Baby" playing in the background to hurry them on.

Even a 10-minute shopping trip for yogurt turns into love on the run for these masters of the horizontal mambo.

Yet real love has little to do with this story that unites a commitment-phobic medical student (Portman) and a low-level producer on a "Glee" rip-off.

Right from start,  "Ghostbusters" director Reitman uses this screen time to mull over an age old question.

Can you have sex regularly with a person and avoid falling in love?

On the up side, Reitman's answer does touch on the times. It also highlights the problems that can arise when commitment and meaningful human interaction get multi-tasked between a zillion tweets.

The movie's premise inspires a few good laughs, at least for two minutes. The rest of the time "No Strings Attached" plays out like a predictable TV sitcom, dishing out one-dimensional cheese that barely pleases.

The film also leaves audiences to ponder this great mystery. Why would "Black Swan's" Portman, the favourite in this year's Oscar race for Best Actress, headline and produce this 10th-rate mess?

No chemistry between Portman and Kutcher

This sex-buddy comedy begins 15 years in the past, when Emma and Adam were teens at summer camp.

"My parents just divorced," Adam cries silently.

"I'm not good at emotional stuff," Emma confesses, putting her arm around this kid for comfort.

"Can I finger you?" Adam asks.

Self-assured Emma slams that idea and time marches on.

Years later the two reconnect. The reunion happens after Adam discovers that his TV-star dad (Kevin Klein) has been sleeping with his ex-girlfriend.

Stunned, wounded Adam calls every woman listed in his BlackBerry for sex. He wakes up hung over and naked in Emma's apartment.

Nothing sexual has transpired, although Emma's med-school roomies try to make Adam believe it has. But when the couple is left alone years of repressed lust explodes on the screen.

Clothes are strewn. Breathless sighs are panted. Emma's roommate pounds on the door, yelling "You've 10 minutes to get to the hospital."

"You've got 45 seconds to get it together," Emma challenges Adam.

Her pal complies and gets Emma thinking. What if they only met for sex?

"Do you think we can do this?" Emma's giddy eyes beam.

Emma's "genius" idea certainly turns these players on. Too bad it can't do the same for this sex-capade with no soul.

"No Strings Attached" is better than most romcoms of this ilk, and Portman does her best with the cookie-cutter material in Elizabeth Meriwether's script.

But I wonder what could have happened here if an actor like Jeremy Renner or James McAvoy had filled Kutcher's shoes.

At the very least, "No Strings Attach" would have delivered some real surprises and steered Oscar contender Portman far, far away from earning a Razzie nomination for this lame farce.

One and a half stars out of four.