CRUELTY
(as) hard as nails
very hard; cold and cruel. (Refers to the nails that are used with a hammer.)The old loaf of bread was dried out and became as hard as nails.Ann was unpleasant and hard as nails.
dog-eat-dog
a situation in which one has to act ruthlessly in order to survive or succeed; ruthless competition.It is dog-eat-dog in the world of business these days.Universities are not quiet peaceful places. It's dog-eat-dog to get a promotion.
in cold blood
without feeling; with cruel intent. (Informal or slang. Frequently said of a crime, especially murder.)The killer walked up and shot the woman in cold blood.How insulting! For a person to say something like that in cold blood is just horrible.