Absolutely zero new ground is broken in “Life of the Party,” a slapstick college comedy with PG-13 hijinks that include booze-soaked frat parties, mean girls getting their comeuppance, a couple having sex in the school library, a group of characters eating chocolate that turns out to be laced with powerful weed and then going bananas, etc., etc.

Even the mom-joins-her-daughter-at-college storyline owes a debt to “Back to School” (1986), with Rodney Dangerfield as a middle-aged dad crashing son Keith Gordon’s university and wreaking all sorts of havoc.

And yet, I’m giving “Life of the Party” three stars — a solid B, if you will — on the strength of at least a half-dozen laugh-out-loud moments, some truly sharp dialogue, a tremendously likable cast and the sheer force of its cheerful goofiness.

The movie is a lot like Melissa McCarthy’s occasionally overbearing, shamelessly corny and indefatigable character of Deanna. At times, we roll our eyes and wish we could be somewhere else, but more often, it’s kinda great to be around something so comforting and lovable and irresistible.

“Life of the Party” opens with McCarthy’s Deanna and her cheap, impatient and jerky husband, Dan (Matt Walsh), dropping off their daughter, Maddie (Molly Gordon), at Maddie’s sorority house for her senior year at Decatur University.

Dan and Deanna haven’t even made it off campus before Dan stops the car and tells Deanna he wants a divorce — and in fact, he’s in love with Marcie (Julie Bowen), a local real estate agent.

Two decades ago, when Deanna was pregnant with Maddie, she dropped out of Decatur U. just a year shy of getting her degree in archaeology. Deanna has a chance to return to school and get that degree, and also spend some quality time with her daughter. Come on, what young woman WOULDN’T want to spend her senior year at university with her mom?

Exactly.

One of the joys in “Life of the Party” is the unexpected turns it takes within the framework of familiar scenes. When Deanna makes her first visit to the sorority house and seemingly embarrasses Maddie with her enthusiasm and her over-sharing (and just being Maddie’s mom in such a setting), it’s reasonable to expect Maddie’s friends to be horrified, but they take an instant liking to Deanna and embrace her as their friend. Nice!

Even the scenes that fall flat or go over the top aren’t entirely disposable, thanks in large part to a deep and talented cast. At any moment, a Jacki Weaver or a Stephen Root or a Maya Rudolph or a Chris Parnell or a Heidi Gardner will pop up and deliver a terrific line or do a perfect double take. Other standouts include Gillian Jacobs as Helen, who’s a decade older than her sorority sisters because she was in a coma for eight years, Luke Benward as a sincere hunk with a major thing for Deanna and Adria Arjona as a gorgeous sorority girl who does not play the stereotypical gorgeous sorority girl.

Directed by the very funny Ben Falcone (McCarthy’s husband) and written by Falcone and McCarthy, “Life of the Party” is harmless good fun. And sometimes, that’s enough.