Period comedies set centuries ago are difficult to pull off, perhaps because the sensibilities of a time so far in the past don't exactly lend themselves to modern-day humor. For every "Monty Python and the Holy Grail," there are countless woebegone failures like 2009's "Year One." "Your Highness" tries, as most do, to blend the medieval with the subversively current (anachronistic speech is in plentiful supply), but the film is otherwise so meandering, juvenile and desperate that when an occasional funny moment slips through the monotonous cracks it proves to be more an exception than the rule. Filled to the gills with explicit scatologia, gay panic, physical slapstick, female ogling, and pot jokes, the movie is forever stuck within the mindframe of an immature high schooler who hasn't yet grown beyond a grade-school mentality. What director David Gordon Green (he of 2008's smarter weed comedy "Pineapple Express" and any number of piercing indie gems like 2008's "Snow Angels") is doing slumming it here is anyone's guess. He's racked up a sparkling cast, to be sure, and then proceeded to rape them of their luster.

Lead actor Danny McBride (2009's "Land of the Lost") and writing partner Ben Best are responsible for the screenplay, its genesis reportedly beginning as a college game where they first came up with a title and then tried to create a silly story around it. Indeed, "Your Highness" feels like something that was devised on the spot, so slapshot is it. McBride stars as slacker Thadeous to James Franco's more handsome, heroic Fabious, sibling princes who head off on a perilous journey to rescue the latter's virginal bride-to-be Belladonna (Zooey Deschanel) after she is kidnapped by evil wizard Leezar (Justin Theroux). Seeking guidance from cheerful molester the Great Wize Wizard (voiced by Mario Torres Jr.), who tells them they must procure an enchanted blade made of unicorn horns to defeat Leezar with, Thadeous and Fabious eventually team up with tough, beautiful warrior Isabel and in no time are battling dangerous creatures and backstabbing comrades as they edge closer to their destination.

Solid production values are but minimal respites to the general clunkiness with which "Your Highness" has been made. There are a few very sparse laughs sprinkled throughout, including the aforementioned scene with the sleazy, fey Great Wize Wizard and another outrageously perverse moment that brings new meaning to the term "fairy dust." For the most part, though, the viewer sits uncomfortably through a barrage of lazy comedic attempts met with utter silence by the audience. Ideas with potential, like the early establishment that Belladonna is naive to the world around her due to being locked up her whole life in a tower, are promptly forgotten about as soon as they are introduced. The sight of Thadeous falling down stairs while dressed in a suit of armor is as deadeningly lame as it sounds. His later decision to castrate a Minotaur and wear its penis as a necklace is so appalling it doesn't even earn any shock value. The quest Thadeous, Fabious, Isabel and lanky squire Courtney (Rasmus Hardiker) make is further brought down by slow, overstretched pacing, battle set-pieces that all but forget it's a comedy and become tedious hodgepodges of barely connected edits, and an overall laid-back apathy.

Comic acting is an underrated art form; no matter how goofy things get, it is up to the performers to treat the material with straight faces and a commitment that makes them and their actions believable. This cast, as fine as they usually are, can't hide their understandable indifference to a project that couldn't possibly have been seen as anything other than a frivolous paycheck filler. James Franco (2010's "127 Hours") smirks and strikes valiant poses as Fabious, but honestly doesn't get much to do. Danny McBride is a bit better as Thadeous, if only because his role is slightly more fleshed-out and the glimmer in his eyes suggest he's having a good time. As Isabel, Natalie Portman (2010's "Black Swan") does play things seriously, and that's why, despite having a next-to-nothing role, she gets a few of the bigger laughs when her stalwart character suddenly utters frank, out-of-left-field sexual dialogue or talks in amusingly over-the-top terms about the future quests she plans to go on to avenge her family (one utterance about burning a tribe alive, their pain signified by a "symphony of shrieks," is a hoot). Otherwise, it's perplexing why Portman took on a project that barely warranted a theatrical release and should have probably gone direct-to-video. As for poor Zooey Deschanel (2009's "(500) Days of Summer"), director David Gordon Green has no idea what to do with her Belladonna, who sits around as if she's perpetually waiting for new script pages.

Erect creature penises or not, "Your Highness" is a limp misfire, depressing in its waste of talented filmmakers both in front of and behind the camera. Bereft of sincerity, the movie is one without a single relationship—not between brothers Thadeous and Fabious, not between lovers Fabious and Belladonna, not between the guys and butt-kicking Isabel—indelible enough to care about or take stock in. They are flimsy constructs who do not live or breathe, but waft with the wind of a narrative that writers Danny McBride and Ben Best treat as an afterthought lark. They toss plenty at the screen and hope it sticks, but little does. It's just as well. There is next to nothing in "Your Highness" worth remembering, but a whole lot one would prefer to forget.