One of the forbidden forms of behavior is cursing one’s parents, whether while they are live or after they have died.
Honoring Parents
כִּי אִישׁ אִישׁ אֲשֶׁר יְקַלֵּל אֶת אָבִיו וְאֶת אִמּוֹ מוֹת יוּמָת וגו': (ויקרא כ:ט)
[G‑d instructed Moses to tell the people,] “Any man who curses his father or mother must be [tried and] put to death [by the court].” Leviticus 20:9

Honoring parents – at least to some extent – is the classic example of a type of behavior that seems so logical that we would have behaved that way even had G‑d not commanded us to. The reason why G‑d nonetheless commands us to observe such rules is that what comes naturally to us, be it good or bad, is limited by human nature. By making otherwise self-understood behavior into Divine commandments, G‑d enables us to go beyond our natures. The Torah thus frees us of our human limitations, enabling us to partake of G‑d’s infinity by revealing our infinite, spiritual essence.1