I see this goof often enough that I think we’re going to lose this battle, (but if you write anything the least bit expository (you know—when you explain something (which this blog is about, after all))) you should use the correct word, regardless of what everybody else does. (Okay, I could have written a less convoluted sentence there, but I thought it would be fun to nest a couple parentheses.)
Anyway, the bad word is nauseous. At least it is when you mean nauseated.
The rule: nauseous means you (or something) makes people want to throw up. Nauseated means you (or someone) feels like throwing up.
Don’t be nauseous to us who know better! We don’t like to feel nauseated!