With my DH, it's not cars, it's "investment/business opportunities". I'm not being supportive if I tell him we shouldn't use our savings to start a new business, or invest in a "can't fail" investment idea, etc..... And this is an educated, intelligent guy who makes great money!
In the past, DH one job to take another where he was being promised a part ownership in a business that was sure to be worth millions in a couple years. Luckily, we made sure to get a contract stipulating DH's salary and getting moving expenses reimbursed.
After, two years of being treated like crap and getting nothing that was promised verbally, DH decided to start his own consulting business because he was tired of working for someone else. Well, the two contracts that he had on the table (from different companies) suddenly disappeared after we'd invested in a new computer and other business equipment.
So, after 6 months of living off our savings, we had to move across the country for DH's new job. This job pays well, has great benefits, and the company treats DH great.
But, DH is now on an investment kick. He's sure he could make great money day-trading and we're sure to be millionaires shortly after he starts trading. I told DH he could have $4000 to play with. Of course, I get told that I'm not supportive because I'm skeptical and unwilling to put our retirement funds or the kids' college money into the latest scheme. I told him, "Hey, if it's a sure thing, then you can prove it to me with $4000 just as easily as you could with more!"
Luckily, my DH wouldn't spend/invest money without discussing it with me anymore than I would do those things without discussing it with him. And I handle our family finances and make sure that we're able to sustain any losses.