4. Juices and smoothies.

Lots of people, from random weirdos on the internet to your yoga teacher, will tell you all about how juices and smoothies are for your overall health. And it's true, they're not terrible for your health, but they're really terrible for your teeth. The sugar in them doesn't do you any favors and they're incredibly staining, especially green smoothies and smoothies with berries.

Related: 8 Common Things You Should Never Keep In Your Bathroom.

5. Tea.

Black and brown teas are the ones most typically called the worst teeth stainers, but green tea can leave stains as well. A great way to avoid tea stains is to gently brush your teeth 30 minutes after drinking the tea.

6. Cough syrup.

Here's one I never ever expected. Cough syrup, the bright orange and dark purple stuff, might help your cough and sniffles but they're loaded with sugar that can quickly cause deterioration of the enamel. Opt for them in pill form, or don't take them all together. They aren't exactly good for you.