Let’s face it: Hollywood producers know that a bad script does not always guarantee dismal box-office returns (how else can we explain the success of movies like “The Saint?”). However, in the case of the new comedy “Half Baked,” it seems as though the creative team behind the hilariously stupid “Billy Madison” may have bitten off more than they could chew.The premise is paper thin. When a childhood pal mistakenly feeds a diabetic police horse junk food and winds up a “cop killer,” three buds rack their remaining brains cells for a way to spring him from prison. The plan? Sell marijuana to the people of New York to raise bail money, of course.Though having the potential to be the Gen-X answer to the “Cheech and Chong” movies in its promising early scenes, “Half Baked” quickly becomes mired in tired cliches. How many times does the eternally-stoned Brian (Jim Breuer) really need to confess his love for weed to elicit a laugh? And is it absolutely necessary to include a ruthless drug kingpin (Clarence Williams III, Link Hayes of “Mod Squad” fame) as the main opposition to our heroes’ unconventional “fund-raising” campaign?Writers Dave Chappelle and Neal Brennan seem to advocate a fantasy world where everyone ‹ even the police ‹ loves dope, but the clunky, first-person narrative of Chappelle’s Thurgood character does little to further their cause. A somewhat promising love story gets lost in the film’s abrupt scene changes, and the finale quickly devolves into what could be an outtake from Chris Farley’s “Beverly Hills Ninja.”Despite the disappointment of “Half Baked’s” one-joke storyline, there are a few high points. Chappelle (“Con Air”) has a charming, everyman screen presence that defies the restraints of an ill-conceived script, and Harland Williams’ (“Rocketman”) jailbird character proves to be the film’s most genuine comedic performance.In the end, it’s impossible to ignore the bad aspects of “Half Baked.” Celebrity cameos from the likes of Snoop Doggy Dogg smack of soapbox preaching on the virtues of marijuana use, and the inclusion of teens sharing a joint is sure to send anti-drug groups into collective fits of rage.Should anyone choose to see “Half Baked,” be ready to leave your brain (along with your hard-earned cash) at the door. You should expect more from the people who gave us a 27-year-old third grader.