Who wouldn't want a watch that not only tells time, but improves your health?

That's the dubious pitch entrepreneur Ryan Naylor brings to the tank with his Esso Watches -- watches that purportedly use negative ions to increase energy, balance and flexibility. At first, things are going swimmingly for Naylor, as he demonstrates the watch's potential on Shark Lori Greiner. Lori, who goes from skeptic to semi-believer after balancing on one foot while wearing an Esso Watch, even remarks: "That's a little weird!"

But Mark Cuban is not having it. As Naylor attempts to pass out his watches for the Sharks to try on, the billionaire curtly declines, even though the model he's offered is in "Dallas Mavericks Blue."

"I'm allergic to scams," the brash businessman spits back.

Watch as Cuban skewers this salesman, leaving little doubt to those who think they can pull a fast one over on him.