Sweet candy - Candy sweets, especially hard candies have tons of sugar which is bad for tooth health since the sweet can cause cavities and get stuck in the crevices causing more bacteria.
Tea and coffee - The tannic acids in coffee and even in some teas can wear down enamel and stain your teeth brown. While you cannot give up tea or coffee completely, try to keep it to the minimum and opt for green tea too.
Pickles - We all find pickles tasty and great as accompaniments to our meal, but the combination of super-acidic vinegar and sugar is a recipe for enamel erosion.
Citrus fruits - Lime, Lemons, Oranges, and Grapefruit, they all are loaded with citric acid which can cause enamel erosion and tooth decay. If you cannot completely avoid them, try to minimize it by avoiding too much of acidic foods and drinks through the day. The best way to find out an acidic food is to see if any food or drink easily stains the teeth.
Soda - Soda has a combination of sugar, acids, and carbonation which is too bad for teeth since it leads to tooth erosion and decay.
Wine - While studies show a glass of red wine every once in a while can be good for the heart and cholesterol levels, the beverage can stain teeth quite easily. The acids in red as well as white wine wear down the surface of teeth, which is why stains are so common.