Coke is an idiot.

There, I said it. Whether you instinctively agree with the statement or not, though, perhaps you want a few more details, so here goes. Today's issue of The Wall Street Journal describes a fast-growing cultural phenomenon, in which amateur video-makers around the world have taped the explosive results of dropping a piece of Mentos candy into a bottle of Diet Coke.

Wrote the Journal: "The combination results in a geyser of soda that shoots as high as 20 feet into the air."


Tiny Mentos, a unit of privately owned Perfetti Van Melle of Italy, says it's "tickled pink" by the phenomenon and, in investigating its popularity, has discovered about 800 videos of the chemical reaction posted on the Internet. Working some back-of-the-candy-wrapper numbers, Perfetti says the free advertising being posted on the Web is probably worth in the neighborhood of $10 million to the company -- half of its annual U.S. advertising budget. When Coca-Cola (NYSE:KO) was asked to comment on the science experiment, however, its response was more muted: "It's an entertaining phenomenon ... [but] doesn't fit with the brand personality" of Diet Coke.

Now, it's no surprise that mighty Coke, with its $2 billion-per-annum advertising budget, isn't as thrilled as Perfetti is with the pop-goes-the-geyser phenomenon. Ten mil in free advertising or no, the exploding-soda phenomenon may hit a bit close to home. Back in the '80s, both Coke and Kraft (NYSE:KFT) subsidiary General Foods suffered at the hands of a disturbingly similar urban legend. Supposedly, General Food's Pop Rocks, combined with a glass of Coke, made Quaker Oats (now PepsiCo (NYSE:PEP)) poster boy Mikey's head explode.

So forgive Coke if its first response to the Mentos trick is something other than "ha, ha."

But really, guys (I'm speaking to Coke now), isn't it time to put the Pop Rocks thing behind you? For one thing, everybody knows it was a hoax. For another, it's been, like, 23 years. Chances are, most of the kids dropping Mentos into 2-liter Coke bottles today weren't even born yet back then. And for a third ... did I mention how cool this Mentos thing is?

Seriously, Coke shouldn't be giving Mentos the cold shoulder here. Coke should be partnering with Perfetti to turn this into The Fad of the Summer of '06, staging performances of the version of the experiment in public parks, and selling not just Mentos and Diet Coke, but other relatives from the firms' respective brand families to enthralled audiences. This is the kind of free, viral marketing that a clever company like Hansen Natural (NASDAQ:HANS) would have been all over months ago. That Coke passes it off with a "pshaw" and a "can't-be-bothered" helps explain why, unlike the Diet Coke-plus-Mentos geysers, Coke's stock has lain flat for five years.

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Fool contributor Rich Smith does not own shares of any company named above.