The term commonly used to describe someone who doesn't care about others' feelings is "callous" or "uncaring." Such individuals may be insensitive, lacking empathy, and indifferent to the emotions and well-being of others. They may prioritize their own needs and desires above those of others, showing little concern for the impact of their actions on others' feelings. In more severe cases, a person who consistently lacks empathy and disregards others' feelings may be referred to as having "antisocial" or "psychopathic" traits, though it's essential to note that a clinical diagnosis would require a comprehensive evaluation by a qualified mental health professional.