"Super Armor" Passive?

I think it's be interesting to see a literally unstoppable champion.

What I mean by this is that their passive makes them "unflinching", as in CC does not stop them. Perhaps only if they are in the process of doing something (I.E. casting, AAing). Basically, the champion would shrug off hard CC and be unaffected by them. However, to keep this from being ridiculous, shrugging off the CC would put them on a (relatively short) timer in which they can be hard CC'd.

Basically this would be a passive for an enormous behemoth, maybe some guy in a crap-ton of armor, or someone made out of unbreakable material. I think it'd be an interesting concept for a tank to be literally nigh unstoppable, though the timer where they can be hard CC'd would be ample counterplay.

I don't think anyone is like this yet, and I think it'd be interesting to build a kit around a champion who throws himself into harm's way to soak up disables and knock-ups, perhaps while dishing out his/her own.

I don't know how soft CC (slow, silence) would affect the champion--maybe they would be affected as normal, maybe not at all? I think being affected by soft CC would be fine.

If this idea interests anyone, I might design something around it, or feel free to use it in your own designs (if perhaps giving me the briefest hint that I inspired it :P)