满不在乎 is a fixed four-character phrase meaning 'not care at all' or 'to be completely indifferent'. It is used as a predicate, often with a negative connotation, implying that someone is unconcerned about something that others think is important. The phrase is not separable and cannot take an object directly; instead, use a preposition like 对 (duì) to introduce the thing not cared about.