It's true that your finances are no one else's concern, but that doesn't mean they won't try to make it. I agree that if you want to buy the car, and can afford it, go ahead and buy the car. But the difference is that depending on the situation, other people may feel a certain way about it. It does go both ways, with stories of people judging their attorney/doctor/accountant etc. if they're driving a beater and seem like maybe times are tough.
An example that a friend of mine asked about was how I felt driving into one of my volunteer activities, where the average person helping out struggles to make ends meet. Obviously, the fact that I'm there means I care and what I drive has nothing to do with what I do with my time/finances to help others, but that doesn't mean that some people won't think (falsely) that I'm just trying to be something I'm not, and that if I really wanted to help, I could donate more money than I am. Again, it's really none of their concern, but that doesn't mean they don't make something of it. And it doesn't have to be direct comments like
@Ahzuz, it could be side comments or moments when you feel they're treating you differently than they did before.
Before my MS, when I bought my GLC, my boss drove a ~10 y/o Honda Accord. He obviously could have upgraded, but didn't feel the need. He was completely cool about it. However, a previous manager of mine mentioned he didn't know how I could afford it knowing how much I made. It was a casual comment, and he was mostly joking since he could easily have done some quick math and realized that as a DINK family living where I lived, it wouldn't be hard to believe that I had a few extra hundred dollars a month to put towards a car based on my salary. But if I had a cheaper car...that wouldn't have happened. My friends and I used to joke that it'd be hard to ask for a raise when managers make comments like that.
There are a lot of situations, work or outside of work, where people make certain assumptions about you and your intentions based on your car/jewelry/clothing etc. Nothing is saying you can't make that decision to wear/buy those, but in our society they are often used as signals, and like any other signal, can be miscommunicated/misunderstood.
I kid you not, as I was writing this response, a (different) friend texted me asking how I got so 'rich' (in response to a recent pledge I made to a non-profit we both work with). I told them, I'm not rich, I've just been lucky with some good jobs and gotten comfortable with certain forms of debt, and made certain decisions with where I want to allocate my money. This was after a recent ride I gave them in my MS, so I find it hard to believe that comment was based out of the relatively small (<$300) pledge I made.
If nothing else, driving a "flashy" car can lead to some awkward conversations that you might otherwise not have. Even those of us who don't have people judging them do have those responses prepared for if/when someone asks about the price. Because it's a thing.