After watching “School for Scoundrels,” I couldn’t help thinking about a comment made by the director Todd Stephens in regards to marketing. “As a director your inclination is to control everything. But then you really have to let go and let people do their jobs and hope they know more about selling [your movie] to an audience than you do. I still wouldn’t have shown Ben Stiller in the ads. I think that was a mistake.”

I can’t help but agree with him. Stiller is only in the picture for a little more than five minutes or so, but his appearance is one of the most raucously comedic masterstrokes of the entire year. In fact, it’s the best the dynamic performer has been in ages, elevating this otherwise forgettable motion picture to a level it hadn’t come close to achieving up until his revealing.

But the moment is severely undercut by the fact, thanks to the film’s commercials and trailers, you know it is coming. There is no surprise when he finally shows up, no shock or awe that the guy opening the door into a life of severe disappointment and acres of cat food is the famous star of “Meet the Parents” and “Zoolander.” What should have been cause for celebration and applause is instead one only for polite laughter, the actor’s near-brilliant cameo wasted because of a marketing department eager to spill secrets in the desire to achieve a bigger opening weekend.

Too bad, because I have this weird feeling I would have been willing to cut “School for Scoundrels” a little bit of a slack had I and the rest of the audience not known Stiller’s appearance was coming. For the most part, writer/director Stephens and frequent co-writer Scot Armstrong have crafted a moderately amusing comedy that is immediately forgettable upon exiting the theater. It’s startlingly flat, a picture enlivened intermittently by its cast of comedic masterminds but not long enough to keep my interest start to finish.

Roger (Jon Heder) is a New York City meter maid plagued with low self-esteem. He’s the kind of guy who gets robbed by the people he gives parking tickets to, has fatherless children turn him down to be their big brother and faints at the thought of asking out his sexy next door neighbor Amanda (Jacinda Barrett). He’s a mess certain to go nowhere, and unless something happens to awaken the confident man hiding somewhere within Roger is destined to be a nobody for the rest of his life.

Enter Dr. P (Billy Bob Thornton) and his mysterious assistant Lesher (Michael Clark Duncan). These two run a top-secret class that transforms its graduates from lemmings to lions, the unorthodox methods behind his success sure to give these losers the tools they need to achieve their dreams. But when Roger proves to be one of the best students in the history of the class, Dr. P’s competitive side kicks into high gear.

Suddenly the teacher is doing all he can to destroy rather than improve his pupil’s life, even going so far as to start romancing Amanda. With time running out Roger rallies others in the class to his cause, and with the aid of a former student he’s going to takedown the master using his very own tricks of the trade. But Dr. P has legerdemain hiding up his expensive sleeves his student hasn’t anticipated, and if the former hypochondriac can’t roll with the punches and improvise he’s going to lose the love of his life forever.

The basics are here for success, and Thornton certainly has a few moments (which, especially an adoption comment that had me rolling, I can’t help feel were probably improvised) of genius that certainly are cause for celebration. In the end, however, none of them ever add up into anything remarkable. “School for Scoundrels” is stunningly conventional, so many intriguing avenues for comedic bliss left unexplored with the filmmakers instead taking their characters down roads I’ve already seen too many times before.

Heder is quickly becoming a one-trick pony. Wonderful in “Napoleon Dynamite,” he was rather bad in “Just Like Heaven” and he was even worse in the otherwise not that bad “The Benchwarmers.” Other than one priceless bit with some lobsters and a show-stopping scene with a Cherry Danish I didn’t like him at all, the actor so monotone and unremarkable I kept imagining how much better the film probably would have been with someone else as the lead.

The rest of the cast does what they can, scene-stealing bits by David Cross, Sarah Silverman, Matt Walsh, Horatio Sanz and Todd Louiso certainly helping Phillips’ cause. But only Stiller rises above the material to deliver something chaotically uproarious, and thanks to the fact we know he’s coming even this brief bit of genius is diluted to a state not near as wondrous as it could have been. Too bad, because “School for Scoundrels” had potential, but like the cast of screw-ups at its core it just can’t live up to it.