[After a brisk nap]

I think tone has everything to do with it. Noir is pessimistic, fatalistic. The characters are morally bankrupt, and any character who tries to take a stand for something is invariably defeated or forced to sacrifice what he most desires. Film noir traditionally goes with a specific visual style. One key marker of film noir is the femme fatale, an enigmatic and treacherous anti-heroine.

I'm sorry, but I've seen the film, and people who call it a noir are mistaken. It's no more film noir than The Big Lebowski is. Like Lebowski, it's certainly very aware of noir, and exists within the wider tradition of hardboiled detectives, which it spoofs as well as conforms to.