I hate "business casual" too. I'd reccomend a blouse with a collar, some sort of blazer (just make sure it's not boxy or like it would fit a man, nothing irks me more than when women look lumpy and shapeless, which my mom does every day despite my protests), a skirt around knee-length, dark nylons, and tall flat boots. And a cute necklace! Or something like that. I'm seventeen and don't have much experience with business casual, but I think a look like that could be pulled off without being too boring or too youthful, so long as you get a blazer that freaking fits and stay away from any colors and patterns that are too bold.