Antonyms for the phrase "doing a favor" include refusing, denying, declining, neglecting, ignoring, overlooking, and withholding. These antonyms indicate an absence of assistance or support, and suggest that the person in question is unwilling or unable to provide aid. Refusing, denying, and declining suggest that the person has been asked to perform a favor, but has chosen to say no. Neglecting, ignoring, and overlooking suggest a lack of awareness or concern for the needs of others. Withholding suggests that the person has the ability to help, but is deliberately choosing not to do so.