Clyde loves to sit on my shoulder and chuckle in my ear and sometimes nibble on it, too, but lately his favorite thing is to pull at my shirt, and in plucking at my shirt, he often gets skin, too. Or he'll go straight for the skin. He's done this so much that he's learned to say "ow!" and "quit!" from hearing ME say it.

Now, I know he's just playing and he also does that if he thinks I'm not paying enough attention to him, but when I object to it, he makes his grumbling "doggone it, I'm BUSY!" noise and usually nips even harder. So I tell him if he's going to gnaw on me, he has to go back to his cage. He doesn't want to go back to his cage, so by the time we get there, he's leaning against my cheek saying "awwww" and "pretty bird" and making kissing noises. Little stinker. I'm sure he knows that I don't enjoy being a chew toy, but I don't know how to make him stop doing that other than the trip back to the cage, because after that he usually stops or is at least far more gentle about it. I'm a sucker for the cheek lean and "awwww" and if he'll promise to be nice, he doesn't have to actually go back in the cage. The trip there is just to inform him that I'm tired of being nibbled on.
And he doesn't like head scritches, either. That's a SURE way to get gnawed on. He likes very gentle strokes down the back if you stop before you get to his tail feathers. I'm thinking the people who had him before must have done all sorts of things to make him neurotic about certain things that I'm only slowly learning to recognize.