'Chillingly egregious' is how Dr Amy Gutmann, the head of the Presidential Commission for the Study of Bioethical Issues, described unethical US experiments carried out on Guatemalans in the 1940s (see here).
Egregious means very bad or outrageous. That is what it means nowadays, anyhow, but interestingly, its original meaning, about 500 years ago, was the exact opposite; the early OED definition (now labelled 'obsolete') is 'distinguished, eminent, excellent, renowned, remarkably good or great'. Egregious comes from the Latin word for 'flock' and the original literal meaning was 'towering above the flock'.
The current definition -- the OED's wording is 'remarkable in a bad sense; gross, flagrant, outrageous' -- has been in use for almost as long as the positive sense; for centuries the word was used by different people and in different sentences with completely different meanings. The Dictionary surmises that the negative meaning came about because of an ironical use of the 'remarkably good' sense, although it admits that none of its early citations provide any evidence for that viewpoint.