Can a person be really and truly benevolent, kind and giving yet on the flip side spiteful, hate-filled and vindictive?

I tend to believe a person is either kind-hearted and understanding or plain nasty and filled with hatred. One cannot be both. How can one be a philanthropist, true socialist and generous and then lash out even at his own family with the worst words a human could utter? The individual in question was taunted and teased throughout his life for weight issues and later envied for professional success. Now seems like he is lashing out at everyone for what he has been through – most times aiming the pain at the wrong people.
What surprises me is his genuine generosity, intelligence and kindness. Next moment a torrent of the most hurtful words come out at whoever happens to be the unlucky one. Can we be so good yet so nasty simultaneously?
A number of people have suffered in life in various ways but they do not go and cut others’ feelings into pieces! What really crushed me, was that he used a few things I had revealed in confidence to him against me in front of others. The excuse? “You have to forgive me, I am in poor health and cannot handle my anger.”
So, are most of us angels and demons or just one of the two?