The list of foods including drinks that are bad for your teeth (promoting cavities and tooth-wear) is long. Basically if it is not in its natural form, its not healthy, but there there are some guidelines that will help simplify things.
1) Any drink in a can or from a soda fountain. If you stay away from any drink in a can or from a soda fountain, you will cut out most drinks that are bad for your teeth. Although it is commonly known that Soda drinks are bad because they have so much sugar, it is also very important to know that even the diet drinks are full of acid, some having a pH approaching battery acid, which is also bad for your teeth. Citric acid hiding in drinks like canned iced tea or even energy drinks like Gatorade is also responsible for tooth decay and increased tooth wear. These drinks bathe your teeth in sugar and acid and the pH of your mouth does not return to a normal level for 15-20 minutes after you finish the drink. Exposure time of drinks when you sip them throughout the day may make you cavity prone for most of the day. Water is always the best drink for you.
2) Candy, cookies and cakes - the worst candy for your teeth being hard candy. Hard candy comes in as the worst kind of candy because of the exposure time. If you suck on the candy, it could be in your mouth for upward of 15-20 minutes, but if you break down and chew it up, the same candy will be in the grooves of your teeth for the same amount of time. Candy is very high in simple sugars. This kind of sugar is the favorite kind for the germs that live in your mouth and make cavities. You should always brush and floss your teeth immediately after these foods.
3) The worst tooth stainers are Tea, Coffee and Wine. Although these will not cause tooth decay or wear, they will cause staining which makes the teeth look old and yellowed. Although not as bad as canned drinks, these drinks are surprisingly acidic too.