Cutouts are a big trend and I bought a cute dress that shows a bit of ribcage. Never okay in the office, right?
Correct, assuming that you mean a conventional office, or even a somewhat creative one, and not your upstairs studio, a corner café or a retail setting in which you are trying to sell this rib-cage dress.
If you sat near me at the office, your peekaboo patch would make me want to reach out and poke it, especially if you were wearing on the dresses with kidney-shaped cut-outs that Guillaume Henry designed for Carven this spring. And we don't even know each other. This is not an appropriate dynamic for a professional setting.
If you want to don the dress for work, why don't you layer a sweater or blouse overtop. Sure, it won't have the same impact, but the office is no place to provoke a poke.