Here's a crazy one for you!

Last week, I was looking over my online credit card statement. (Conveniently, this card has a web site where you can view transactions up to the last business day.)
I noticed a charge of around $18 for a pizza. I recalled buying a pizza from this same pizza place over a month before, when I was over at a friend's house - but not since then. I double-checked, and yep - they already charged me for that pizza last month, so this was a new charge.

I filed a fraud complaint, but then I realized what really happened. When I ordered the first pizza, they updated their computer to link my card number to my friend's house address (without asking me first!). Then, when my friend ordered his own pizza last week, they charged it to my card number, on file, instead of to his own card!