If you go to a “Harold & Kumar” movie, you should know what to expect: tons of raunchy gags and visuals, plenty of politically incorrect humor, outrageous and often violent slapstick, broad, wide-eyed turns from the leads, and Neil Patrick Harris sending himself up. And wall-to-wall drugs, of course—drugs in amounts that would choke Cheech and Chong.

If that’s your cup of tea, this third installment in the series may satisfy you. But you should notice that one major item is lacking in the above list of ingredients—laughs. “A Very Harold & Kumar Christmas in 3D” is raucous and vulgar and frantic. But despite all that it’s surprisingly limp and unfunny. Even the Harris bit—he’s not really gay, dude!—is a bust.

Of course, the movie—like its predecessors—is just a string of episodes strung on the weakest of foundations. This time around, at the beginning the guys have become estranged, with Harold (John Cho) a straight-laced Wall Street type married to a Latin hottie (Paula Garces) and living in the suburbs, while Kumar (Kal Penn) remains a pot-head slacker who was tossed out of med school for failing a drug test. But when a package for Harold is delivered to their old apartment on Christmas Eve, Kumar decides to drop it off at his old partner’s house. It turns out to contain a huge joint, and when Kumar lights it up, it sets Harold’s Christmas tree ablaze. And that tree—home-grown, no less—was provided by his hostile father-in-law Carlos (Danny Trejo), a holiday fanatic.

So the duo set off to find a replacement tree, an odyssey that gets them into all sorts of trouble, sometimes also implicating Kumar’s nerdy, horny neighbor Adrian (Amir Blumenfeld) and Harold’s uptight pal Todd (Tom Lennon). There are sketches involving faux homeboys, a family of Russian gangsters, a holiday pageant, a robotic appliance called the Wafflebot, lots of weed, cocaine and sex, exposed penises (one in claymation, of all things, and another stuck to an iron pole), flying feces, Santa Clauses (both fake and real), and even a party-boy Jesus (though the funniest line in the sequence involving the last was unaccountably omitted in the final cut, though included in the trailer). The puritanical will be shocked, even offended, by bits that constitute mild blasphemy, crude ethnic stereotyping, nudity, and child endangerment—so you’ve been warned.

But the real problem with the movie isn’t that it’s offensive—it’s that it comes across as more pose than genuine article. Like the clumsy Cheech and Chong pictures that it’s emulating, it just drifts along in a haze of sweet-smelling smoke, offering gags that are meant to be hilarious but are so stumblingly executed, and then endlessly repeated, that they will elicit laughs only from viewers who are stoned themselves. The first “Harold & Kumar” picture had a real sense of risk to it; this one seems half-hearted. It goes through all the expected motions, but without much energy, and the tastelessness comes across as mere calculation. There’s very little that exhibits any imagination or daring, and when the movie lumbers to an end, it’s a totally conventional one that celebrates family, marriage, and pregnancy. How establishment is that?

The same thing applies to the performances. Cho and Penn look tired of these parts, and give them only the bare minimum effort. Trejo does his familiar angry shtick but no more, and Elias Koteas is trapped in the part of a gangster so stale that he’s a caricature of himself. Harris’ turn is far less funny than his previous ones, and when he alludes to a possible fourth picture it comes across as an unhappy threat. Old friends from the previous films like Eddie Kaye Thomas and David Krumholtz show up, only to flail around for a few minutes, delivering unfunny lines. The only standout is the Wafflebot, but even its battery goes low very quickly.

“3D Christmas” boasts a bigger budget that the earlier installments, and turns the format itself into a joke while using it persistently to poke you in the eye with a huge penis, thrown eggs or shattered bits of glass. But there, too, it all seems rote, though professionally executed. A movie like this needs some sense of risk if it’s going to matter, but “A Very Harry & Kumar 3D Christmas” only risks putting you to sleep. It probably will have disappeared from theatres by Thanksgiving.