Whereas gangsta rap’s essential gambit is to make cartoonish fictions play as “4 real,” mainstream American action movies flip the formula: They provide plenty of genuine-looking violence, softening it with ironic humor. One of the originators of this recipe is Shane Black, who briefly became a movie-biz legend by writing (and selling) the script for 1987’s Lethal Weapon when he was just 23. Black’s reputation faded as subsequent projects flopped, and he vanished altogether after 1996’s The Long Kiss Goodnight, as Quentin Tarantino became Hollywood’s new master of the sardonic bloodbath.

So it’s to be expected that Black’s rebirth as a writer, and debut as a director, is as heavily footnoted a genre-mocking exercise as Pulp Fiction. Kiss Kiss, Bang Bang takes its title from a collection of writings by film critic Pauline Kael, its chapter headings from Raymond Chandler, and the style of its opening credits from ’50s and ’60s animator/designer Saul Bass. The result is bustlingly self-amused, and the movie’s pleasure in its own cheekiness makes it fun to watch, if not to ponder.

After a prologue set in innocent Indiana, Kiss Kiss, Bang Bang introduces its central character, Harry Lockhart (Robert Downey Jr.). Or rather, Harry introduces himself—as not only the film’s narrator but also its demiurge. Like any respectable Mel Gibson character, Harry gets brutalized repeatedly. Yet his misfortunes can never be taken seriously, because he’s in charge of the story: He can interrupt the action, rewind the narrative, cue the flashbacks, and interject digs at Drew Barrymore’s sex life, so you have to wonder why he doesn’t just hit Pause every time he’s about to get thrashed.

As Harry explains, he’s a small-time thief who, while running from New York cops, blundered into an audition. Improvising on his actual situation, Harry impressed the scout, who had him sent West for a possible movie role. In Los Angeles, Harry is apprenticed to homosexual gumshoe Perry van Shrike (Val Kilmer), aka Gay Perry, who’s supposed to show Harry how real PIs work. But Perry’s tutorial intersects an actual murder case, and soon Harry is courting danger in earnest—or as earnestly as a movie this contrived can get. The homicide also entangles actor Harry Dexter (Corbin Bernsen), who used to play hard-boiled detective Johnny Gossamer on TV, and aspiring actress Harmony Faith Lane (Michelle Monaghan), who just happens to be Harry’s classmate and teenage crush from back home in Indiana. Although Harmony eventually claims that Tinseltown has brutalized her, she doesn’t look it. (In fact, the 29-year-old Monaghan appears, oh, about 11 years younger than the 40-year-old Downey.)

Aside from Harry’s glimpse at the naked crotch of a female corpse, the movie’s sexual content is entirely PG, and strictly for giggles. (Gay Perry is gay mostly for the sake of his punning name.) What really earns the flick an R is its gross-out material, including lots of play with a severed finger and that cadaver, which just won’t go away.

For all its absurd complications, the plot is ultimately unsurprising and not all that interesting. But the film’s playful energy is contagious, and some of the nastiest bits are capped with amusingly self-deflating gags. A showcase for Downey as much as Black, Kiss Kiss, Bang Bang does considerably less for Kilmer and Monaghan. But the star’s likability takes a hit during the final credits, which feature a number by would-be modern-cabaret singer Robert Downey Jr. For this attempted comeback by a writer and two actors who peaked too soon, couldn’t they have spread the karmic wealth by using something from Axl Rose?