We’ve been counting down the year’s most-read mentalfloss.com stories. First we rattled off #20 to #14. Then came #13 to #6. At long last, here are the five most popular stories of 2009.

5. Why Does Bottled Water Have an Expiration Date?
by Matt Soniak
Why do bottles of water have a “drink by” date when common sense dictates that water doesn’t go bad? Blame New Jersey.

4. 4 People With Super Memory
by David K. Israel
What if you finished reading this article and remembered every detail of it for the rest of your life?

3. Why is 10:10 the Default Setting for Clocks & Watches?
by Matt Soniak
Reader Humaira Baig wrote in to ask why clocks and watches are always set at (roughly) 10:10 in the store. Here’s the explanation.

2. Symbolism and the $1 Bill
by Ethan Trex
Crack open your wallet, pull out everyone’s favorite portrait of George Washington, and be prepared to learn about some odd symbolism that probably seemed perfectly normal in the 18th century.

Drumroll…

1. 10 Secret Menu Items at Fast Food Restaurants
by Stacy Conradt
At Fatburger, you can order a ‘Hypocrite’ — a veggie burger topped with crispy strips of bacon. Here are some other secret menu items from across the country.

That was the story that landed us on The Today Show:

Here’s to learning lots more crazy stuff in 2010!