Greetings @luna2!
Thanks for sharing your question- first of all, I’m so sorry you have to deal with all of your roommate’s negativity. It sounds like his life habits are causing a lot of stress for you, which is really hard to deal with in your own living space 
I have to agree with what others have mentioned about thinking very carefully before choosing to cast a curse (suggested guide on that here). I personally categorize curses and hexes as Baneful/Black Magick (that is, magick cast with the intent to hurt or bring harm to people or things), which is against my personal code of ethics. However, not everyone follows the Wiccan Rede or believes in karma/divine retribution/etc- it is up to you to decide what to do, based on your own system of ethics and beliefs.
Even if I don’t suggest casting a curse, you do have a legitimate problem on your hands and I’d like to offer some possible spellwork that might help you. I believe that Black Magick and White Magick (healing/wholesome magick) are two opposites, and that for any curse that could be cast, the same problem could be solved in a different way with wholesome spellwork.
I don’t think your real problem is the car here, I think that the actual underlying issue is your roommate’s inability to do anything- so to address that, here are some magickal options you could take:
Cast a Good Luck Spell
→ Either for your roommate (to get the job/money in order to repay you) or for yourself (to be less affected by his actions or potentially that he moves on without any conflict)
Cast a Freezer Spell
→ Freeze his toxicity and bad behavior by neutralizing his negativity
Cast a Banishing Spell
→ Banish his bad energy (or perhaps his entire presence) out of your way
Just a few suggestions you could consider, Luna! I’m wishing you all the best and I hope the situation resolves soon.
Blessed be! 