The mundane film “Standing Still,” about a group of college friends who reunite for a wedding, is here to show us how the anxieties of young adulthood (mainly romantic ones, shared by good-looking people) can all be resolved in the course of a single weekend, provided that ample booze is served and enough heart-to-heart conversations take place – preferably sooner than later, just so, you know, everybody’s fully sorted out in time for the ceremony.

Set, appropriately, in Southern California, this ensemble effort would like to be both a colorful blend of entertainment and gravitas for the 20-something set. But it ends up as a predictable trifle propelled exclusively by pop music, popped corks, and sexual possibility.

“This weekend’s gonna be pure hell,” Lana (Mena Suvari) sighs, buying a handle of rum in preparation for the big night-before at the sumptuous house of the bride and groom. Her life’s a bit chaotic at the moment – too much sleeping around – and she’s not looking forward to running into her ex-boyfriend Sam (Johnny Abrahams) at the party. Cut to Quentin (Colin Hanks), who takes the optimist’s view as he tries on his tux: “This weekend’s gonna be ridiculous!”

Actually, there’s no reason to get so worked up. The weekend proceeds to shape itself into a perfectly trite, paintby-numbers profile of privileged young adults that’s quite free of hilarity. Guests and their hang-ups are introduced, usually at the same time, by way of brisk exposition. Elise (Amy Adams) is trying to get her fiance, Michael (Adam Garcia), to open up about his broken family before they exchange vows; Rich (Aaron Stanford) and his longtime girlfriend, Samantha (Melissa Sagemiller), are arguing about whether they should tie the knot; Quentin, an agent, has brought a new friend into the circle, a hotshot young actor named Simon (James Van Der Beek) who appears to have a serious drinking problem. And just to keep things interesting, a very attractive lesbian (Lauren German) has flown in from London. She arrives clad in a thin shroud of mystique (Ms. German’s character is the only non-blond female) but quickly doffs it to make out with the bride.

Such an abundance of characters may justify a certain shorthand approach, but “Standing Still” is so loath to focus on any one person (or couple, even) that a shameless cliche of a montage sequence – a bachelor party in Vegas cross-edited with a bachelorette party in the living room, set to Joan Jett’s “Bad Reputation” (also featured on the soundtrack to “10 Things I Hate About You”) – is actually refreshing for its willingness to sustain a theme.

The truly startling thing about this film, which presumably attempts to resemble real life, is the utter absence of adults. The lone exception is the groom’s unwelcome, formerly abusive father (Xander Berkeley), who’s miserably camped out in a hotel nearby. Otherwise, the bride and groom have conveniently been scripted as orphans. One might expect an adult relative or two to show up as the moment of betrothal nears, but the only late arrival here is the bride’s sister, a teenage sexpot who seduces Quentin on the spot.

That a film about becoming an adult should be unabashedly – even vengefully – adolescent is not necessarily unintentional. The new clout of the teen market may be defining the current era of mainstream movies more than we care to admit.

But good teen movies, like “Can’t Hardly Wait” and “American Pie,”don’t lie about what they are. What’s more, they acknowledge that high school doesn’t last forever, whereas “Standing Still,” which claims to be about adults, is guided from beginning to end by the same puerile fantasies born between Algebra and Home Ec class.