“Your Highness,” the latest collaboration between director David Gordon Green and screenwriter-actor Danny McBride, is a silly, stylized genre mash-up. Equal parts medieval fairytale, adventure story and buddy (read: stoner) flick, it consistently settles for bawdy humor, lacking the cleverness that drove their previous film, “Pineapple Express.” Hilarity ensues; just don’t let your expectations run away from you.

Set in a fictional faraway land, “Your Highness” is a tale of two brothers questing after love and the security of their kingdom. Prince Fabious, played by an overtly homoerotic James Franco, is renowned for his courage and chivalry, while his younger brother, Thadeous (McBride), prefers to spend his time womanizing and smoking “herbs.” When the evil sorcerer Leezar (Justin Theroux) crashes Fabious’ wedding and kidnaps his new bride, Belladonna (Zooey Deschanel), the two princes immediately set out to rescue her. Along the way, they encounter Isabel (Natalie Portman), a mysterious warrior who also has a score to settle with Leezar. I won’t ruin the finer details of the quest, but suffice it to say that the road to Leezar’s lair is paved with treachery, pedophilic wizards, bar fights and a tribe of grimy naked women that bear a strong resemblance to Ke$ha.

Overall, “Your Highness” can only be described as highly ridiculous, and I mean that with respect to every sense of the word “ridicule.” While it functions well as a self-aware comedy, its weak writing prevents it from rising to that upper echelon of humor: parody. Whereas “Pineapple Express,” to which “Your Highness” pays homage through Thadeous’s recreational use of plants, cleverly exploited popular culture and traditional narrative conventions, this new iteration continually goes for, and achieves, cheap laughs. Hence what begins as a spoof of the medieval quest gradually devolves into increasingly crass vulgarity (think the “Scary Movie” franchise versus “Tropic Thunder”).

But what the film lacks in wit, it more than makes up for in titillating absurdity. For one thing, the amusement of anachronistic uses of the F-word never wears off, particularly when it results in novel phrases like the “fuckening,” a reference to the prophecy by which Leezar taking advantage of the virginal Belladonna will result in the birth of a dragon that threatens to destroy the entire kingdom. The gaudy special effects also contribute to story’s ludicrousness, not only in the visual manifestation of Leezar’s magical powers, but also in the representation of mythical creatures, such as an unusually horny minotaur.

While acting generally takes the backseat to the novelty of the story in movies like this, I would be remiss in not acknowledging the mismatched cast. Franco and Portman, both highly recognized this past awards season for their roles in “127 Hours” and “Black Swan,” respectively, go all out in “Your Highness.” Franco’s charm and sexuality shine through as the kingdom’s golden boy, but Portman’s portrayal is the most compelling, for as Isabel, she successfully achieves that elusive combination of female empowerment and bad-assness sans the sexual objectification that most action movies can’t seem to avoid (including and especially the recent flop “Sucker Punch”). Thadeous, on the other hand, is not so much an actual character as McBride’s usual comedic persona, only this time with a British accent.

All told, “Your Highness” is an entertaining ride, at times sidesplitting, and at others merely cringe-worthy. The collision of genres is perpetually dysfunctional, but perhaps therein lies the appeal. But if nothing else, the film, which despite having wrapped production in 2009 is only now hitting theaters, is a light-hearted vehicle for its biggest stars, Franco and Portman, whose performances remind us to never take anything too seriously.