When does “No Strings Attached” lose all credibility? When its second scene allegedly takes place at a frat house at the University of Michigan and the frat house is loaded with pretty California girls. I went to Michigan. There’s a longstanding saying at Michigan. Nine out of ten girls in the Big Ten are attractive. And the tenth goes to Michigan. How do I account for Lucy Liu? I suspect she’s lying.

The question about Natalie Portman’s career has always been how an actress can seem like such a natural as a child and then have such a hard time as an adult. The short quip is that Harvard ruined her. The longer answer and my current guess, as evidenced by her recent round of movies, appears to be that she is a good but limited actress who specializes in emotionally frigid characters and controlled personalities. That makes her perfect for a role like “Black Swan.”

In theory, it makes her perfect for the role of this film’s emotionally frigid and controlled doctor, after an emotionally-condom-covered sexual relationship with Ashton Kutcher. But it also makes the character all wrong for a romantic comedy. An actress might be able to pull it off if she could exude a reserve of likable warmth that makes her a rooting interest. That actress isn’t Portman. It doesn’t help that she’s paired here with indie it girl Greta Gerwig (of Greenberg), whose presence is immaculately natural.

Needless to say, controlling is not the first word in comedy, even if “No Strings Attached” offered any actual opportunity for it. Whenever there is a chance Portman shows no natural spontaneous instinct for it. Her actions always have the taste of Elizabeth Meriwether’s script. Whatever facility for comedy she showed in “Garden State” is not in evidence.

As for the rest of Ivan Reitman’s film: it’s not warm. It’s not sad. It’s not cute. It’s not funny. It’s not true. It’s not even enjoyably false.

It’s just not.