In Chinese culture, labeling someone or something as 残忍 (cánrěn) is a severe moral judgment. It directly opposes the core Confucian value of 仁 (rén), which means benevolence, humanity, and compassion. To be 残忍 is to be fundamentally inhumane and lacking in the basic empathy that holds society together. A useful comparison is to the English words “mean,” “strict,” and “cruel.”
残忍 (cánrěn) is used in both formal and, occasionally, informal hyperbolic contexts.
It is almost always negative and is a very strong word to use against someone directly unless you are making a serious accusation or joking with a close friend.