Concept
In this universe, depending on the obsessions that you have, your body gets slowly taken over by your vice(s).
Ideas
Here's how I envision this. If you are an obsessed cardician, your genital will start transforming into a deck of cards or into a pad, a card case or a single playing card. Your hair will change colour depending on the deck that you're practicing with. When you fart it will sound like the riffling of cards. When you sneeze like springing a deck. Depending on how you feel, you will get a different deck as a genital each day.
If your vice is smoking cigarettes, your genital might transform into a cigarillo, a filter or a pack of smokes. If it is to transform into a pack of smokes, you will always have a supply of cigarettes with you. When the pack is finished, it just becomes replenished. The trick is that the taste of these cigarettes will be influenced by how you treat your body, what you eat/drink, how you sleep. Your facial hair is slowly morphing into rolling tobacco. Your nails into rolling paper.
The Procreation Problem
Now, as a writer, you are going to take this a step further and think: these people want to procreate. How can somebody with a deck of playing cards as a genital procreate? They would need someone with a card case or a pair of hands as a vagina. If their genital is a piece of paper, then a pen or a brush would do, but definitely not someone with a pair of scissors.
This could be a way to filter who you are compatible with and who you're not compatible with. If I have a flash light as a dick, I will definitely not go out with someone who has a mirror between their legs.