Christmas is a week from today. Which means, depending on whether you count today, you've got either six or seven days left to shop. Good thing, too—I know that I, for one, need all the time I can get.

But this isn't a gift guide. I'm not going to talk about the specifics of gift giving, or some fun new product on the market that makes a great gift. That's coming later this week. The purpose of this column, rather, is to tell you that there are certain categories of gifts that come with rules. Not even necessarily the southern, old-fashioned rules. Just, you know, rules.

Jewelry
Friends can buy each other jewelry. Family members can buy each other jewelry. But you need to be really, really careful before you buy jewelry for your significant other. Fun, trendy jewelry is one thing, but I'm talking "fine" jewelry: gemstones, precious metals. Diamonds. Do not get your new girlfriend diamonds. Any gift of jewelry is seen as a sign of serious commitment. It's an investment. Not just in the gift, but in the future: you don't want that girl to flush your three months' salary down the toilet if things don't end well.

Appliances
Gifts are supposed to be fun. Frivolous, even. So unless your friend has been dying for a new rice cooker because he makes killer sushi, you shouldn't be giving someone something that feels like work.

Subscription Services
You told your parents that you can't live without your DVR, and they seemed interested. So you decided to get them a Tivo. That's all well and good, except that now your parents—not the most technologically-advanced folks—are not only left with figuring out the Tivo for themselves, but also with the subscription fees for years to come. If you want to give the gift that keeps giving—from your pocket—then by all means, get your parents the Tivo. Otherwise, stay away.

Generic Gifts
Sure, everyone can use a warm scarf, but running into Old Navy and picking one up doesn't mean you put much thought into your gift. Gifts should show a degree of thought about the recipient, and you should know that the recipient probably thinks that they say something about you, too. Think before you buy, or, if you're at a complete loss, get a gift certificate. It's generic and boring, sure, but at least the recipient will have the opportunity to choose his own gift, rather than dealing with the bad one you picked out.

Cash
Cash is a perfectly acceptable gift if you're giving a bar mitzvah gift or graduation present. Provided that you're at least ten years older than the person you're giving the cash to. Getting cash from one's own peers feels wrong. And just a little dirty. If you're at a loss, get one of the aforementioned gift certificates, or even a pre-paid bank card that can be used wherever major credit cards are accepted. Just stay away from cash—or checks—unless it's less a gift and more a payment for services rendered.