Once, in an effort to improve upon a terrible cup of coffee provided to me somewhere, I tried adding the non-dairy creamer, Coffee Mate I think it was, to it. Big mistake. It made bad black coffee even worse.
- It's called non-dairy whitener, or coffee whitener, in other parts of the world (such as the UK, it looks like) so that you don't think it's really cream. Really, it's artificial cream with vegetable oil.
- They may not be completely non-dairy: most of them contain casein, which comes from milk, in order to make it, well, milky. Which matters if you're allergic to milk (rather than lactose intolerant) or vegan.
- You can make a fireball with it! One of the ingredients can become flammable when dispersed. Tested and confirmed by Mythbusters.
- It generally seems to be made up of things that are not food - edible, maybe, but not food. Basically, it's high fructose corn syrup, hydrogenated vegetable fat, casein, artificial flavoring and colors, and phosphates. There are rundowns here and here.
- It's not good for you. The worst offender in the ingredient list is the partially hydrogenated oil, also know as trans fat. The coffee creamer container may say "No trans fat!" on it, but labelling rules allow you to say a product as 0 grams of trans fat as long as it has 0.5 grams or less trans fat per serving. But if you end up using more than one serving of creamer, you could end up getting quite a lot of trans fat. And no amount of trans fat is good for you.
- It comes in a lot of flavors. A LOT. International Delight alone has 22 flavors on their website. Is creaminess not enough of an addition to one's cup of coffee?
- The worst sounding flavor: Cinnabon. I can't think of anything worse than adding the flavor of horrible, airport/mall cinnamon rolls into my coffee cup.