At one point, the notion of Seth Rogen as a father was so inherently ridiculous that they made an entire feature-length comedy about it. The curly-haired Canadian/marijuana enthusiast has always seemed like every straight American male’s platonic ideal of what a best friend should be: smart, funny, ready to dispense advice and/or drugs at the drop of a hat and loyal without crossing the increasingly blurry line into homoerotic dependency that so many of these bawdy flicks end up walking (because hey, no homo, right guys?). He has never, though, been anyone’s idea of dad material. The guy frequently looks like he just rolled out of bed, how are we supposed to believe he could rouse a toddler out of his crib? Not to mention nearly every Rogen movie is a loving paean to the joys of staying eternally young, and also the build-up towards that inevitable moment where our lovable schlub is finally forced to grow up.

Turns out, everyone’s favorite chuckling Jewish teddy bear has grown up. Well, sort of. He actually plays a dad — and, from the looks of things, a (mostly) decent one — in “The Night Before,” a shambling, sporadically funny stoner comedy that splits the difference between your traditional yuletide yarn and the typical Rogen gross-out-fest where friendships are tested and eventually affirmed, naughty jokes are made and everything turns out to be more or less alright in the end. More often then not, the movie succeeds — even if it practically evaporates as you watch it, which is why it’s probably best to do so with a sack of strong sativa in hand. Three days later and I can’t remember many of the best jokes from “The Night Before,” save for a killer third-act Jay Gatsby shout-out and an extended sequence where a sweaty, paranoid Rogen trips out on a combination of mushrooms and MDMA and dedicates a hilariously hateful video testimony to his unborn son. But the movie itself is sweet and silly, with a lightness of touch. However flimsy it is in the grand scheme of things, in the moment it possesses a modest but undeniable charm.

Our trio of bros this time around are Isaac, (Rogen) Chris (Anthony Mackie) and Ethan (Joseph Gordon-Levitt). Isaac is the typical Rogen nebbish gone domestic, Chris is a charismatic, hot-headed football superstar with an all-too-predictable secret and Ethan works dead-end catering gigs and remains emotionally stunted after the tragic and untimely death of his parents. With each passing year, their brotherhood of bong hits and bar crawls is solidified by one longstanding Christmas tradition: a night of karaoke, Chinese food, playing the piano from “Big” at F.A.O. Schwartz and, finally, the attempt to gain access to the Nutcracka Ball, a mythological party that is reputed to be one of the most lavish and elusive in New York City. A few things end up complicating the boy’s quest, however, including the re-emergence of Ethan’s old flame (the wonderful Lizzy Caplan) and Isaac’s wife giving him a pocket-sized box of narcotics (little bit of weed here, a smidgen of cocaine there) that he ingests all too willingly. Throw in a gang of drunk sidewalk Santas, an admittedly rousing live performance of Miley Cyrus’s “Wrecking Ball” and an almost-too-creepy cameo from Rogen’s pal James Franco, then roll, seal, spark and inhale and you’ve got “The Night Before”.

The director here is Jonathan Levine, who helmed the soulful hip-hop Sundance comedy “The Wackness” and also “50/50,” (his first union of Rogen and Levitt) a flawed but ultimately affecting dramedy about one young man’s battle with cancer. Levine has a gift for naturalistic comedy and an ear for male banter and camaraderie, and “The Night Before” is certainly less ephemeral than something like, say, “The Interview,” even if it never matches the devastating human moments of Levine’s earlier, better films. It doesn’t hurt that our three stars manage to convincingly portray a lived-in, long-term friendship marred by instances of doubt and betrayal. Rogen is especially funny when he’s losing his shit, although a nasty gag about cocaine blood ending up in a woman’s drink goes too far, while Mackie subtly oscillates between bouts of self-aggrandizement and the crippling insecurity of a grown-up jock. Not surprisingly, Joseph Gordon-Levitt turns out to be the film’s heart: his Ethan is a palpable and heartbreaking vision of young male stasis, even when the film’s busy script saddles him with some unwieldy expositional dialogue. “The Night Before” also features a who’s who of up-and-coming comic talent in supporting roles, including the indispensable Jillian Bell as Rogen’s no-bullshit wife, Nathan Fielder as a weirdo limo driver, Mindy Kaling doing Mindy Kaling, “Broad City’s” Ilana Glazer as a weed-stealing Grinch and Tracy Morgan in a role that is way too funny to spoil here.

So it’s a shame that “The Night Before” isn’t more substantial than it needs to be. The movie is often sloppily paced, careening from one wild, raunchy set piece to another with little regard for narrative coherence. The movie is admittedly less reliant on insipid pop-culture name-dropping than other films in the Apatovian vein, and therefore more likely to have a shelf life. What’s most disappointing about “The Night Before,” really, is that it actually does flirt with some dark and interesting ideas, before ultimately backing safely away from them — as if the studio was afraid to reveal genuine layers of depth in pain in what’s supposed to be just another goofy Seth Rogen flick. The notion that poor, damaged Ethan is clinging desperately to his two remaining pals — both of whom have aged more or less gracefully into adulthood, and who could both probably get along just fine without their co-dependent friend — is a genuinely intriguing idea, and one deserving a more nuanced treatment then the slipshod one found here. Knowing that Rogen, Levine and company are capable of a more psychologically graceful work than this makes the loss all the more bitter.

But no matter. In almost every respect, “The Night Before” is exactly what it’s supposed to be: a broad, big-hearted trifle whose momentary lapses in good taste are ultimately redeemed by its sweetness. And it does boast at least one totally unforgettable character, one who will surely earn his place in the annals of holiday movie legend. That would be Mr. Green, the boy’s old neighborhood pot dealer, played by one of the scariest actors currently working, Michael Shannon. Here, Shannon dials back the insinuations of menace that characterize his best performances and leans hard on the gentle, old-soul qualities of his screen persona, playing a man who thinks nothing of comparing himself to the hero of an F. Scott Fitzgerald novel and who lovingly tells his customers (or his “children,” as he prefers to call them) that he’s proud of them for continuing to smoke the ganj well into their 30’s. Imagine if everyone involved in making “The Night Before” had taken a cue from Shannon’s loopy, self-aware turn here. Then we’d have a real Christmas miracle on our hands. C+