It's also worth mentioning that an MITM proxy with a private CA root certificate could just strip HPKP headers out of any webpage it sends you. If your computer

It's also worth mentioning that an MITM proxy with a private CA root certificate could just strip HPKP headers out of any webpage it sends you. If your computer is tied to its network (e.g. corporate PC) it will never see it, so there's no issue.