Did I do wrong? Opinions welcome!

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So today my sister's boyfriend was driving home from work and their car broke down, they managed to get it up the garage but they didnt know if it would be done by tonight for him to go to work. So she phoned and said to my mother that she was going to ask me to lend him my car. I said no, now there are a pile of reasons why so I'll explain them: - He drives like a maniac, seriously he doesnt really care about speed limits, he always seems to be in a race. Right now it is also snowing and there is a lot of ice around so its dangerous driving conditions anyway but he doesnt change his driving for the conditions, so its even more dangerous, but he thinks driving in the snow and ice is fun! I dont want my car getting damaged. - He doesnt look after the car. Their car is full of rubbish from his takeaways. He works on a security site and instead of sitting in the small office he prefers to take a blanket and sit in the car. So he is also eating and drinking in the car as well, Im not the type of person who goes crazy about crumbs in cars but I dont want to be finding bits of burgers and left over chips in my car as I do like it looking clean. - The site he works on is full of stones and mud, sounds silly I know but he drives fast on the site and then stones get flicked up by the wheels and hit the car, and it also gets filthy. Im not being petty, although if you read my discussion on mud then you might think Im getting obsessed. I know cars get dirty but if I have to drive through a muddy field then I would go slow and not drive like an idiot to get the car covered in mud. I said to my sister that if she needed my car to go shopping or if she needed to take the baby somewhere then she could have it, but not him with the way he drives. I dont even talk to him anyway because of his disgusting behaviour at a family party a while ago, but I am civil to him for my sisters sake. This probably did influence me when saying no but I really dont trust him driving my car. He might not feel the need to look after their car because they havent paid for it all yet. My mother paid for the car as they needed one when my sister had her baby, they are paying back a little every month and still owe her money from it. Whereas I paid for my car and worked in a job I hated to save the money up to pay for it. Which is why I look after it. Its not like I was his only option to ask anyway, Im not the only one who can help them and they sorted something else out, but my sister was annoyed that I wouldnt help. Im now thinking that I should have gone against my instincts and said yes, as I dont want my sister to think she cannot ask for help, and had it been her that needed the car I would have said yes. What do you think? All opinions welcome!