1. The skin on the back of your knee-cap.
2. A black version of the monsters from "Where the Wild Things Are."
3. A slang term for a blue African Avatar that smells and emutes juices
4. The act of acting like a baby
1. Yo, I can see your nefferbilly.
2. Watch out! There's a herd of nefferbillies coming!
3. Sandra, you reaked today, did a nefferbilly get to you?
4. Joey, you need to stop acting like a nefferbilly before I hit you.