I've worked 'office casual' for years. In practice, years ago that meant smart trousers / skirt and a reasonably smart top. Smart-ish jumpers allowed in the winter and a lot of people dressed up casual with suit jackets.
Current employer is office casual, but not 'no jeans'. We have everything from 14" skirts, jeans and a Thomas Pink shirt (the jean wearers tend to be label wearers) to 3 piece suits. I find myself utterly confused by the best way forward in this environment.
I have occasionally taken advantage by wearing jeans, top and a wool blazer when I need to go somewhere casual after work, but otherwise jeans is always a 'dress down Friday' thing in my head (and even then, in some organisations, 'dress down at your peril' Friday).
So, does your office casual allow jeans? If my boss and her peers occasionally rock up in jeans, should I? WTF is office casual anyway if a pair of bootcut (I know, but I am small and curvy) jeans and a cashmere sweater don't raise an eyebrow?