Science Fact: Guys are more likely to make impulsive spending decisions if they believe that available women are scarce.
Explanation: If you're a guy, and one without a ton of money, you've probably been in a situation where you spent some of it solely to look good (or magnanimous, or friendly) for a girl. "Oh, I'll get these, ladies," you'll announce, whipping out your wallet to pay for everyone's coffee. You open up your wallet as suavely as possible, and it contains nothing but a moth and a crumpled up receipt from the moth store. You ask the cashier if she accepts moths, and she informs you that she does not.
For once, we can't relate this phenomenon directly to cavemen, but we can tie it to the late 1800s, when an economist first coined the term "conspicuous consumption." Up until then, almost everyone who was rich had always been rich, but suddenly, for the first time, there was such a thing as becoming rich. The people who did so went around buying solid gold monocles and ancient Egyptian top hats as a way of saying "Look at me, I'm cool too!" Money became one way to woo The Ladies, and it worked well enough that even an orange goblin, sufficiently well-financed, can keep spontaneously marrying people. The flipside is that when there aren't many women around, guys apparently start jockeying for position by just straight-up flinging dollar bills all over the place.
The Science: There's a lot of evidence for this weirdness. One study looked at 140 U.S. cities and found that, the fewer women there were, the higher the rates of impulsive spending (more debt and more credit cards). The same study followed up with some experiments illustrating this behavior; in one of them, researchers asked a bunch of dudes to plan their budgets after reading fake news articles that implied their area either had a large dating pool or few available women. Guys who were told there were fewer women around planned on saving 40% less money.
Later, the researchers showed guys sets of photographs—some with lots of women, some with few women. They didn't even explain the purpose of the photographs, but the suggestion that women were scarce made these dudes go "There are no girls around oh my God I have to rent a blimp immediately" and make an impulsive financial choice (to accept $20 today rather than $30 in the mail).
And if those don't knock your socks off, here's the kicker: men are more likely to make impulsive financial decisions if they merely touch a bra. That's right; the mere reminder that there is such a thing as boobs is enough to make guys go financially bonkers.
So What Should I Do About It?
Well, for girls, the message here is that, generally, dollars=attraction. Some female Sparklers have written in asking about whether or not a guy is interested, when that guy has spent money on gifts, and the answer to this is almost always yes, because most high school guys have a net worth somewhere between several dollars and no dollars.
For guys, here's something to keep in mind: women increasingly like guys because they're fun or attractive or whatever, and not because they're rich. Wealth is nice, but it's not the whole ballgame, so don't splurge on some kind of ostentatious nightmare because you imagined the vague concept of a bra.