Adorkable: Dave is the picture of the well-meaning and kind-hearted dork next door. Even when beaten up. Red Mist also applies, even when surrounded by mafia thugs. In addition, Dave's "fighting style" is meant to be hilariously awkward and dorky, as opposed to the way Big Daddy and Hit-Girl fight.
Aluminum Christmas Trees: The comic asks why people in real life don't become superheroes, and answers, basically, "because it would be stupid." But there are in fact people in real life who put on costumes and go out patrolling their neighbourhoods. They fare about as well as Kick-Ass does (minus the run-ins with the mob), getting injured a lot and rarely confronting any evil worse than purse-snatchers, but the events of the comic aren't as divorced from reality as the comic itself seems to think they are.
Broken Aesop: The main point of the comic is essentially to be a deconstruction about why being a superhero is a completely idiotic idea in real life, with Dave being a massive This Loser Is You, while the book relies heavily on This Is Reality. Except for the story also features the impossibly badass Hit-Girl who, while presented as being not at all well-adjusted, still manages to do things no human could possibly do, and whose memetic badassery is encouraged. It undermines the 'superheroes are a stupid wish-fulfillment fantasy' when there's one who's pretty awesome and not depicted as a loser.
Broken Base: Red Mist'sAlas, Poor Villain moment in Volume 3. Some feel it does humanize Chris somewhat, and he get's a Redemption Equals Death hammered in by the fact that even though he's sorry, Hit Girl dismisses his apology because of all the harm he's caused. Others feel it's a cringeworthy attempt to try to ring out sympathy for a truly hateful character, and tries to bank more on his film portrayal than the monster he's always been in the comics.
Common Knowledge: After the car runs over him, Dave suffered nerve damage that in turn made him inmune to pain... But that's wrong. Dave complains of injuries during the comic. He only gets pain inmunity in the movie (itself a reconstruction of Mark Millar's book). Also, he doesn't get 85% of his skeleton replaced by metal bones (Another thing that just happens in the movie), but just a metal plate in his skull.
Red Mist and his father manage to cross it at the same time, after setting up Kick-Ass and the others. First, they beat the shit out of them. When Hit Girl tries to fight back, Johnny G orders his men to shoot her in the back, which they gladly do, sending her flying out a window. Red Mist then raves about how awesome that was, demonstrating that he's either a total sociopath or at least isn't very good at separating comic books from reality. In either case, that's the moment when both of them stop being mere villains and cross the line.
The revelation that Big Daddy isn't an ex-cop and dragged his daughter into the lifestyle after running away from her and lying to her about the fate of her mother.
Reconstruction: The series becomes less mean spirited over time; Dave becomes less selfish and egotistical, and his faith in Superheroes are rewarded when they give them insight to escape death in the climax of Volume 3. The last shot also recreates the opening scene where a man jumps off a building and dies....only this time he actually flies.
After Kick-Ass gets hit by the car, if you look at his legs, you can see part of the bone sticking out.
Kick-Ass shoots John Genovese in the tunk. You get to see the end of his dick fall to the floor.
Too Bleak, Stopped Caring: Anyone who seems to be in the right is quickly revealed to be naive or secretly an asshole; the main character is a spineless worm who's deluding himself into thinking he can be a hero, while the primary hero character is an utter tool who has turned his daughter into a violent criminal to live out his own dreams. And yet the people they fight against are even worse. There's a reason a lot of people prefer the movie's significantly more idealistic take on the story.
Wangst: Dave's narration can be accused of this. But everyone else has their moments too.
The Woobie: Dave and Mindy suffer a whole lot through the story. Angie Genovese becomes this in Volume 3 where she becomes a social pariah for the crimes Chris did.
Adaptation Displacement: Most people seem to know more about the film more than they know about the comic.
Awesome Music: Flying Home, the BGM track for when Kick-Ass flies away with an exhausted Hit-Girl on a jet pack following the climax of the film. So iconic is the track that it's also the DVD menu theme, and The Riker Maneuver has extended it into a 6 minute instrumental and a lyrical version.
Crosses the Line Twice: A lot more than twice actually. Single scene example: Dave gets stabbed in the gut. The audience winces. He then staggers out into the street and gets flipped by a car. The audience starts laughing.
Draco in Leather Pants: Red-Mist has a lot of fanart. Granted, most of it is from the movie rather than the comics.
Hit-Girl getting shot in the chest when the singer Mindy McCready committed suicide of self-inflicted gunshot wound may be difficult to watch.
During the torture scene, Dave reflects on the fact that he would miss out on seeing what he and Katie's kids would look like. However, in Kick-Ass 2, they break up early in the film.
During Dave's opening narration, he mentioned that since his mother died of an aneurysm in the kitchen, the viewers won't be expecting an "I will avenge you mother!" storyline. This is exactly what happened in the sequel when Chris/The Motherfucker had his father brutally tortured to death.
He Really Can Act: Nicolas Cage surprised a lot of people with his portrayal of Big Daddy. It helps that the movie character is much more sympathetic then the comic book character.
Before Big Joe burns Big Daddy during the torture scene, he says "For all of you cavemen out there, this is called fire" then it cuts to Todd and Marty watching. In 2013, Nicolas Cage (Big Daddy) and Clark Duke (Marty) voiced cavemen in The Croods. In the film, fire is indeed an important plot.
It Was His Sled: The movie makes no secret of the fact that Red Mist is The Mole, whilst it was a twist in the comic.
The scene of Big Daddy testing the bulletproof vest on Hit-Girl by shooting her with a Beretta 92FS became a popular staple of meme comics because of how disturbing it is out of context.
Moral Event Horizon: D'Amico crosses the line when he finds out Kick-Ass had nothing to do with the death of his men but still insisted on him being beaten and executed on a live webcast. The sheer look of sadistic pleasure on his face and the disgusted look Chris gives him when they're both watching it said it all.
One-Scene Wonder: Mr. Bitey had probably less than 30 seconds of screen time, and is still one of the most remembered and oft-quoted parts of the movie.
Rescued from the Scrappy Heap: Pretty much everyone due to the movies making the characters actually sympathetic rather than a bunch of jerkasses. Of particular note are Big Daddy and Red Mist.
Ron the Death Eater: The fanbase tends to prefer the Dave/Mindy ship over the official Dave/Katie, and thus tends to vilify Katie. The sequel makes this vilification canon by making her a Bitch in Sheep's Clothing all along.
What Do You Mean, It's Not for Kids?: While the theatrical trailers for the film show plenty of foul language, violence, and countless other clues that this is not a kid's film, the television trailers are censored. Because of the young ages of the superheroes, there's a chance some parents may get a nasty surprise if they took their child to see it. Since the title of the movie is Kick-Ass, they'd sort of deserve what they got if they did that, especially since the movie is rated R.
, the BGM track for when Kick-Ass flies away with an exhausted Hit-Girl on a jet pack following the climax of the film. So iconic is the track that it's also the DVD menu theme, and The Riker Maneuver has extended it into a 6 minute instrumental