Does God’s description of some people with characteristics such as a dog and a donkey constitute an insult from God, and do these verses justify insults from humans?

To describe Allah Almighty as a "reviler" is a grave atrocity and a tremendous falsehood. The verses that liken some people to dogs or donkeys are parables used to illustrate the state of these individuals in a specific characteristic, not that they are literally dogs or donkeys. This is the difference between reviling and striking a parable. The Quranic parables are of great benefit; Allah guides some people through them and misleads others. As Sheikh Muhammad Al-Muqaddam warned against describing an unbeliever as an animal, the Quran likens but does not describe directly. The fundamental principle is that a Muslim is not one who slanders, curses, or is obscene or vulgar, even with non-Muslims, as the Prophet, peace and blessings be upon him, clarified.