Tosca

This is my cockatiel, Tosca.
He's pretty. He sings. He's an evil little bastard.
Tosca bites. For fun. These aren't love nibbles. He'll grind his beak into you and draw blood. He'll eagerly climb on my hand and tear into a pinch of skin. If I make him perch on a stick he leans over and bites my hand. For awhile I thwarted him by curling my hand into a fist so the skin was too tight to pinch, but he discovered softer skin say underneath.
I'm pretty sure his dream ambition is to put out one of my eyes.
I used to have a civilized cockatiel named Quasi. I bought Tosca so he could have a friend. This new "friend" was such a brute that I had to get him a separate cage. During out-of-the-cage playtime Tosca's favorite game was to sneak up on Quasi and peck his tail. He persisted at this even though it typically resulted in Quasi whipping around and chasing him off the perch. Quasi kicked Mr. Bucket last year. Now I'm stuck a pet who threatens me each night when I have the audacity to put my hand in his cage and change his water cup.
Why do I feed him and keep his cage clean? I don't get it.