The opposite of "thinks highly of" can be expressed in various antonyms such as "disrespects," "disparages," "demeans," "underestimates," or "undervalues." When someone thinks highly of an individual, they esteem their qualities or capabilities. Conversely, when someone underestimates or demeans a person, they diminish their worth or abilities. The connotations of these antonyms suggest a lack of respect or admiration for someone's achievements or character. However, when we think of these antonyms with respect to a person, we should be cautious about making negative judgments, as they are subjective and may not necessarily reflect the truth about the individual's worth or capabilities.