(especially in children's books) make me think of them as much smaller: maybe the size of a cow. But an animal that could easily swallow a cow whole is not one I want pick a fight against, particularly with no real weapon in my hand.
Only a fool chooses the Lord for his enemy. Compared to the Creator of the universe, that crocodile is smaller and less powerful than an ant. He is leaving time now for repentance, but He will bring about justice. When that happens, do you want to be one He is avenging for injustice committed against you, or one He is bringing about justice against for crimes you committed against others? In the meantime, do you really want that person who hurt you so horribly to receive the puny punishment you are able to deliver, or to receive true and full justice from the Lord of all? I certainly wouldn't want to be in the position of over zealously "delivering justice" to someone only to later find the Lord avenging that person against me for my misbehavior toward them.