With the exception of billionaire Bruce Wayne, superheroes must possess a proven superpower to survive the onslaught of the world’s most gruesome criminals. Masked crusaders don’t exist in real life because they’d probably be shot in the face within 30 minutes of their first patrol.

Such is reality in “Kick-Ass,” a funny, ultra-violent riff on what it means, and what it can cost, to be a superhero. Just be sure to leave your cape-loving kids at home for this bloody comic book adaptation.

The film centers on Dave Lizewski (Aaron Johnson), a 17-year-old comic book nut living in crime-infested New York City. After purchasing a green wetsuit online, the moron decides to take his adoration of superhero life to an unhealthy level, transforming into the cute alter ego, Kick-Ass.

Without any form of martial arts or weapons training, Kick-Ass gets himself admitted to the hospital on his very first outing. Luckily, he manages better on his second attempt, and some amateur video of the successful skirmish goes viral.

The YouTube sensation attracts the attention of real-deal superhero Big Daddy (Nicolas Cage, terrific in full-on oddball mode) and his deadly 11-year-old daughter Hit-Girl (Chloe Grace Moretz). Kick-Ass also enrages the temper of a vicious mobster (Mark Strong) and his geeky son, Chris (“Superbad” standout Christopher Mintz-Plasse). Soon enough, Chris dons the persona of Red Mist in an effort to oust Kick-Ass and impress his blood-hungry father.

Director/co-writer Matthew Vaughn (“Layer Cake,” “Stardust”) does an impressive job balancing several tones in “Kick-Ass.” The movie begins as a straight comedy and gradually shifts into a darker vision of real-world heroics (without losing the stylistic action fanboys so crave).

The arrival of Big Daddy and Hit-Girl in the picture only blurs the lines more. As played by Moretz, excellent as the wise, younger sister in last year’s “(500) Days of Summer,” Hit-Girl is as invincible and ruthless as John McClane in “Die Hard.” She gleefully murders her bad guy assailants, taunts them with filthy language and shows no remorse whatsoever.

The character has drawn heavy criticism from parent-watchdog groups and even film critic Roger Ebert. Yet the violence in “Kick-Ass” isn’t nearly as gruesome as the gore seen in movies like “Wanted” and “Sin City” (both were praised by Mr. Ebert). Hit-Girl is a kid, sure, but also a hero living in a world where the only successful superhero is the one that makes sure the bad guys don’t return for a sequel.

A kid blowing away gangsters will either offend you or not, but “Kick-Ass” is much more than one controversial character. The film weaves smart humor into a gripping tale of ordinary people who grow tired of justice teetering so often on the side of evil. Vaughn brings flare to the film’s numerous action sequences, and the performances are all superb (especially from that actor formally known as McLovin).

Based on a little-known comic book by Mark Millar and John Romita Jr., “Kick-Ass” both satirizes and honors the superhero origin tale and does so with an even more defined sense of reality than “The Dark Knight.”

It’s a superhero brand that deserves a multi-film franchise, just so long as they don’t allow some idiot film executive to make it a PG-13.

Grade: A-