Cajetan Boy, a Kenyan writer from Nairobi, showed Vishal Bhardwaj a script about twin brothers from the city's slums in a script-writing workshop held by Mira Nair in 2005.
Boy soon sent Bhardwaj another draft of his script, as the latter thought that it had the material for a masala Hindi film. 3 years later, Bhardwaj bought the script for US $4,000.
Bhardwaj revisited the idea and added some Bollywood elements and a dark, serious side to the script, along with writers Sabrina Dhawan, Abhishek Chaubey and Supratik Sen.
Bhardwaj later said that he included Sabrina Dhawan in writing the screenplay because he thought she would give a 'solid structure' and 'female angle' to the film
Bhardwaj had said that during the writing of the screenplay, most of the original ideas were changed and the climax was 'Indianized'.
The re-worked version of the script included one brother with a stammer and the other with a lisp, which was not there in the original.
Sabrina Dhawan had said that the film's script was complex and has multiple stories which required excessive writing and rewriting to make each character sound distinct.
According to Bhardwaj, despite the complicated structure, Kaminey is 'anything but arty' and would not alienate audiences, and that it is a simple story but with a complicated structure.
The media initially showed concern over the film's title - which can be translated into English as 'mean' or a 'bastard' - deeming it 'odd'.
The makers had defended the title, saying 'kaminey' is not a negative term and is actually a term of endearment.
The idea for the title came from a scene from Gulzar's Ijaazat (1987), in which the hero refers to the heroine in a loving manner; it was the first time Bhardwaj heard it being used in that context
'When the script of this film was written, it was like discovering my own mean side. All the characters in the film, excluding one, has an agenda. So I thought it was an apt title,' Bhardwaj had said
Priyanka Chopra initially turned down the role of Sweety, saying she felt it was a boys' film and her eight-scene part did not seem good enough. However, Bhardwaj persuaded her to accept the role.
Shahid Kapoor worked out for six months and took lessons in stammering from an ENT specialist to fit into his roles in the film
The kissing scene between Shahid and Priyanka was originally not in the script, but Bhardwaj decided to add it because he thought the movie was starting to look outdated and boring.
Priyanka didn't want to do the kiss, though. So she had the director shoot the entire scene without the kiss until she could make up her mind. Finally, she agreed to do it, after Bhardwaj's convincing
Priyanka played this extremely vocal Maharashtrian girl who believed in making herself heard and hence Bhardwaj made sure her voice was heard far and wide for the entirety of the shoot.
Priyanka had much trouble while shooting, and lost her voice multiple times, as Vishal Bhardwaj made her scream her lungs off in scenes involving multiple takes.
Priyanka and Shahid fell off a bike while shooting for Kaminey. The accident took place in Pune on 21st August 2008, while a scene that required Priyanka to ride a bike with Shahid was being shot.
While shooting, Priyanka travelled in a local train, wearing a burqa, from Gorgaon to Churchgate to attend a award function, which was scheduled post the shoot. She was later picked up in car.
The idea for casting the screenwriter Amole Gupte came from the casting director Honey Terhan. Gupte said that when he received a call from Terham, he thought it was a joke.
However, after meeting Bharadwaj and hearing a script reading, Amole loved the story and his character, and accepted the offer.
Kaminey showcased Amole Gupte as an actor after a long time. He is also famous for his paintings in the opening credits of 'Hazaar Chaurasi Ki Maa'. He also cowrote the screenplay of Taare Zameen Par.
For the role of drug dealer Tashi, Bhardwaj chose his friend Tenzing Nima—a tour operator in Mussoorie—saying he had the character and attitude he wanted, and a weird sense of humour.
For the choreography of the song sequence 'Dhan-Te-Nan' in the film, the actors were briefed to 'just dance with the song but not to do any (dance) steps in it.'
The song Dhan Tanan Tana was first used in the title song of the TV serial Gubbare.
Bhardwaj instructed the film's entire cast and crew to watch caper classics such as Two Smoking Barrels (1998), Snatch (2000), Pulp Fiction (1994) and True Romance (1993) to study the genre.
Kapoor said that each role had its own challenges. Charlie's physique was very different from Kapoor's and it took him nearly a year to change the look of his body.
Priyanka learnt the Marathi language for a month to make the character as authentic as possible.
The song in the first trailer is sung by either Vishal Dadlani or Sukhvinder Singh. The singer was kept a secret.
