Antonyms for "dost a favor" may include phrases such as "do a disservice," "harm," or "ignore." When someone does a disservice, they actively work against the interests or well-being of another. Whether intentionally or not, this can result in negative consequences for the person affected. Similarly, when someone harms another, they cause physical or emotional damage. Finally, ignoring someone can be seen as the opposite of doing them a favor, as it involves neglecting their needs or desires. While "dost a favor" implies a positive action taken to benefit someone else, these antonyms suggest a lack of concern or even malicious intent towards them.