What word describes a state that is not sensitive to others' feelings?

The term that describes a state of being not sensitive to others' feelings is indeed "unfeeling." This word indicates a lack of empathy or emotional responsiveness, suggesting that someone is indifferent to the emotions or well-being of others. When a person is described as unfeeling, it typically implies they do not recognize or care about the feelings of those around them, which aligns perfectly with the definition sought in the question.

While "thoughtless" could also convey a similar meaning, it often implies a lack of consideration rather than an outright absence of feeling. In contrast, "unfeeling" directly communicates that there is no emotional awareness or sensitivity at all. "Nonchalant" refers to a calm or relaxed attitude, which does not inherently mean a lack of feelings but rather indicates an aloofness that may involve an awareness of feelings without showing them. "Attentive" suggests a high level of awareness and sensitivity to others, so it does not fit the criteria of the question. Thus, "unfeeling" is the most precise description of someone who is not sensitive to others' feelings.