It’s not so much a rule, as an understanding — an agreement between filmmaker and audience. If your comedy or rom-com is only 80 or so minutes long, you’ve got to give us something to laugh or at least smirk at in the first hour.

“I Used to Go Here” is an enervated laugher in a minor key starring Gillian Jacobs of TV’s “Community” “Ibiza” and “Walk of Shame.” For much of the movie, all that’s demanded of Jacobs is that she look cute and lonely.

She plays a first-time novelist deflated by the news that her book isn’t selling, that her publisher’s book tour has been canceled, and that her ex-fiance isn’t that interested in returning her calls.

And “deflated” is the only note Jacobs hits for most of this Kris Rey (“Unexepected”) comedy.

Kate’s book, “Seasons Passed,” has just come out. She’d love to celebrate, paint the town (Chicago), etc. But while her friends are thrilled for her, most of them seem pregnant and are otherwise distracted. The ex isn’t taking her calls. The publishers are underwhelmed, and their assurance that “a good New York Times review could change everything” is small comfort.

And we viewers know ominous foreshadowing when we hear it.

A call from out of the blue is her salvation. Her mentor at her alma mater down in Carbondale (called “U of I” here, but really the home of Southern Illinois U.) invites her down for a reading, a few days of being lauded and mentoring student writers.

Her “book tour” is how she describes it, in yet another message to the ex. Yay. It’s been 15 years, a little return-in-triumph is in order, and a walk down memory lane.

We sniff out the mentor in an instant. Casting Jemaine Clement in the role seals the deal. This writing teacher falls in the “those who can’t teach” bin, and a cozy college’s tenure will have to do. And even though he’s married, we do wonder about the student he lavishes his attention on (Hannah Marks) and wonder what he and Kate might have shared.

Kate revisits her old rental house, now filled with mild-mannered college boys, stumbles into a classmate and cyber-stalks her ex, who has plainly moved-on. But no matter what she puts out there, how needy and ready-for-a-rebound fling she advertises, the sophomoric sophomores aren’t buying, or are missing the signals.

Actress turned writer-director Rey is an alumnus of the “mumblecore” school of rom-com, films more about the banter than the action. She used to be married to mumblecore king Joe Swanberg.

But while this Aug. 7 release is plenty chatty, it’s not particularly witty, just winsome and sad. It’s starved of oxygen and incident, of funny lines or clever exchanges. Nothing the least bit amusing happens until Kate joins the generic college kids for some over-the-top hijinks, “hijinks” we’ve seen in scores of other comedies — “American Pie” is referenced, perhaps unintentionally.

It’s not grim to sit through, but casting comic talents like Kate Micucci (girlfriend of an old classmate) and Clement sets up expectations Rey can’t or won’t meet.

The movie this most resembles in a most superficial sense is “Liberal Arts,” which sent Josh Radnor back to campus to fall for Elizabeth Olsen. Like Radnor, Jacobs is used to the rhythms of sitcom acting. Like Radnor, she’s trapped in a movie that doesn’t have sparkling writing to rescue her or a particularly interesting character to play.

Like Radnor, she’s waiting for something clever or cute or funny to perform. You can almost see the wheels turning, “Maybe NEXT week’s script’ll be better.”

MPAA Rating: unrated, drugs, sexual situations, profanity

Cast: Gillian Jacobs, Jemaine Clement, Zoe Chao, Hannah Marks, Josh Wiggins, Khloe Janel, Forrest Goodluck and Kate Micucci

Credits:  A Gravitas Ventures release.

Running time: 1:20