Contest Winner Cameo: Kind of, but going a bit beyond it: Dave Lizewski, winner of a charity auction and contest to name the main character, named him after himself. Which is rather fortunate because he could have named the character anything from Betty to Captain Ass if he wanted to.
Name's the Same: Hit Girl's civilian identity, Mindy McCready, shares her name with an all too real, troubled country singer who committed suicide in 2013.
When I was 15, my best friends and I were reading Frank Miller comics, like Batman: Year One. (...) We were so into it, we should have been studying for exams at the time. We wanted to become superheroes like Batman. It was pathetic. We were five years too old really to be doing this. The story was really about what would have happened if we hadn't come to our senses and actually gone out and done this.
John Romita Jr. said that he decided to add personal touches of his own to the series when he found out that the series had a personal connection to Millar. Romita designed the neighborhood, schoolyard, setting, and clothes in a manner that evoked his neighborhood in Queens, New York City; most of the time the series is set in Romita's neighborhood.
Channel Hop: Matthew Vaughn initially went to Sony, which distributed Layer Cake, but he rejected calls to tone down the violence. Other studios expressed interest but wanted to make the characters older. In particular studios wanted to change Hit-Girl's character into an adult.
Creative Differences: Production Designer Martin Childs was fired by Matthew Vaughn, early in the production, because they were "not on the same wavelength". Russell De Rozario was hired as his replacement five days before shooting started.
John Romita, Jr. stated that Big Daddy's story in the film "works better stopping short ... You love him better in the film". Millar stated that the revelation about Big Daddy's background would not have worked in the film adaptation, and "would have ruined the movie."
Dawson Casting: Christopher Mintz-Plasse (Red Mist) and Lyndsy Fonseca (Katie), as well as several other actors, are in their early 20's yet play teenage characters. Somewhat averted with Kick-Ass himself, Aaron Johnson was 19 when the film was released.
Development Hell: The sequel. It was initially announced to be made for a 2012/2013 release but is on hold due to Aaron Johnson taking time off acting to be with his daughter and Matthew Vaughn directing other projects. It's now set to a 2013 release and to be directed by Jeff Wadlow (with Vaughn's blessing/supervision).
It seems that before ending up in Lionsgate Studios, the producers of the movie tried several other studios who all had the same ultimatum: "We'll take it, if you drop Hit-Girl or make her 19." Thankfully, they didn't.
The entire reason Red Mist survives the end of Kick-Ass 2 is because when Mark Millar told Jeff Wadlow (director and writer of the second movie) of the character's death, he argued that they couldn't kill the character off as he's one of the series' staple characters & they couldn't really do Kick-Ass 3 without the character.
The Red Stapler: Hit Girl's dual Benchmade 42 butterfly knives.note Because of the popularity of Hit-Girl and her specific mention of the Benchmade 42 balisong/butterfly knife, combined with the fact that Benchmade had stopped producing the model a few years prior, and the fact it was already a somewhat sought-after knife in collecting communities, demand for the knives far exceeded the supply. Prices for an as-new model nearly tripled what they had been months earlier. Because of this spike in demand, Benchmade retooled and produced a very small number of new limited edition BM42s, which sold for over $1000 each.