What's the one thing I can do to hurt my credit score the most?

Credit adviser Nicole Atchison of Consumer Credit Counseling Service counsels Worldy Armand in Boston, August 2004. See more debt pictures.
John Nordell/The Christian Science Monitor via Getty Images

Credit scores are something of an obsession in developed nations. There are ways to improve them (like paying bills before their due dates), but this takes time and perseverance. You can also seriously damage your credit score -- this can happen quickly, sometimes with only a misstep or two.

Debt Image Gallery

A cottage industry has grown to help people figure out how to navigate the difficult waters of borrowing money without harming their credit further down the road. Books and radio shows have been developed to help people live debt-free altogether. Web sites -- including HowStuffWorks -- dole out advice on how to improve credit scores. Media outlets run stories on everyday people who've been plunged into credit nightmares.

Even with all the credence that's given to credit scores, some studies have suggested that the numbers might not always accurately reflect a person's credit worthiness -- and some of the research is pretty startling. For instance, if your local library engages a collections agency to retrieve a book you never returned, your credit score can drop as much as 100 points [source: CBS4]. That's a pretty significant amount, considering credit scores range between 300 and 850 points.

Even in the domain of credit card companies, there are strange and surprising ways to damage your credit score -- even when you're making a concerted effort to do the opposite. Curbing excessive spending by canceling a credit card can damage your credit score, especially if the card carries a high limit and a low balance [source: BankRate]. This is because credit bureaus use the ratio between your available credit and how much you owe to help determine your credit score. Getting rid of a card with a high limit and no balance can increase your debt-to-credit ratio.

There are myriad ways to turn your sunny credit outlook into a quagmire, but what is the absolute worst thing you can do to your credit score? Find out on the next page.