INGRATITUDE. — It is the disposition of mind (vice) of one who does not recognize or appreciate the benefits received. It can take the form of a purely negative attitude of not acknowledging, not thanking, or not repaying the good received; it can also assume a positive attitude of opposition in one who judges the good received as inferior to his own merit, as a harm rather than an advantage, or repays the benefactor with insults or other injustices.
Morally, ingratitude (the negation of the virtue of gratitude, a specific virtue distinct from piety and religion and a potential part of the virtue of justice) is always a sin. From the perspective of its object, the sin is generally considered venial inasmuch as it does not directly contradict the order of charity; however, depending on the end (out of hatred for the benefactor or contempt for him) or the circumstances (e.g., when someone, though able, refuses to help a person in need after having received notable benefits from them), it can become a mortal sin.
Ingratitude is always a moral fault; in legal systems it is not considered a crime; however, in strictly defined cases, it can be grounds for revoking a donation (Italian Civil Code, art. 801). According to the Code of Canon Law, the records of a Church or its administrators cannot be invoked to revoke a donation made to the Church (can. 1536 § 4).