Why, among the millions of children and adults who grew up idolizing superheroes, has nobody ever tried to become one? That’s the question troubling Dave Lizewski (Aaron Johnson), a nerdy teenager determined to take a bite out of crime in the Big Apple.

Dave doesn’t seem suicidal, though his mission certainly does. Armed only with a green-and-yellow jumpsuit and a modicum of protective gear – intimidating he isn’t – he sets out to live the fantasy and gets a knife in his gut for his troubles. But thanks to a viral video, captured via cell phone and rebroadcast, YouTube-style, to a world of tickled witnesses, his alter ego, Kick-Ass, is an instant Web sensation.

Take that, Spider-Man.

Naturally the field of would-be superheroes, at first thought to be limited to one naïve but courageous soul, is soon crowded, not only by the dynamic duo Hit-Girl and Big Daddy – played with warped charm by Chloë Grace Moretz (Diary of a Wimpy Kid) and Nicolas Cage, channeling Adam West – but by the rogue impostor Red Mist (Christopher Mintz-Plasse, of Superbad). Recognizing his limitations, Kick-Ass accepts their help, but his ill-chosen allegiances land him in the mob’s clutches.

For commercial reasons, it must have been tempting to tone down the dirty language and lurid violence of author Mark Millar’s comic books, but director Matthew Vaughn (Layer Cake) clearly resisted. He gives Kick-Ass an exhilarating edge, and it earns its R rating with gusto. Some might recoil at 11-year-old Hit-Girl’s taste for butchery, or her gift for gab blunt and obscene, but the movie’s bursts of brutality are invigorating, and the humor is both shocking and razor-sharp.

That should be enough to keep younger children out of the theaters, possibly against their wishes. But nobody else who’s ever dreamed of being a caped crusader should miss Kick-Ass, a soaring adventure – and a winning coming-of-age comedy – that contemplates the conflicted life of a masked misfit every bit as thoroughly as The Dark Knight, without the brooding overtones. It’s dark, but hardly tortured.

There will be grumblings that the movie tries too hard, balancing too many plates at one time, but taken on its own delightfully twisted terms, it is bold and uncompromising. It knows its audience, how they speak and think, and delivers a fable for the ages, deliciously uncensored. If that sounds like high praise, so be it: Kick-Ass earns that, too, by living up to its name.