In Genesis 4, Cain killed his brother in a jealous rage, In Exodus 2, Moses slew an Egyptian due to anger over Jewish mistreatment. Stephen was stoned in Acts 7 because Jews were upset by his preaching. Both of those will cause one to be cast to the lake the burns. Godly anger stems from love and righteousness and has in view the good of him against whom it is directed. We can and should get angry at how people abuse God and His name.
Unholy anger comes from pride and desires the injury of another.
This is difficult to define because it describes a tone of voice more than anything else. It is a tone of contempt, arising from anger. The people of the world are often full of contempt, pride in birth, race, position, knowledge, money. Raca is worse than anger because it leads to contemptuous remarks. Fool The 3rd degree of murder is to call someone a fool out of anger and contempt, not the mere words spoken.