They might not know it, but they are drinking 10 teaspoons of sugar.

In addition to its high sugar content, soda is highly acidic and can disolve tooth enamel.  Carbonic Acid creates the bubbles in soda and is also present in all diet sodas, carbonated water, and seltzer water.  Among the other ingredients frequently found in soda are Phosphoric Acid and Citiric Acid.  Acidic drinks can contribute to tooth erosion and tooth sensitivity.