Drinking coke MAY cause yellow teeth [staining your teeth!]. MAY is the codeword though... I've never had yellow teeth and my pearlies have always been acceptable white [even before and way after I got my teeth brightened
] but I always drank regular Coke and diet Coke.
WebMD says:
Foods, drinks, poor dental hygiene, disease, medications, genetics, environment and trauma can cause your teeth to become yellow.
As long as you try to keep your teeth healthy by going to the dentist regularly, flossing, and brush at least twice a day, I don't see a problem.
If you're that worried, just don't drink Coke like it's water. :F IT'S HARD! lol, but you can do it.