As odd as this sounds, try hissing at him and showing your teeth. I've figured out with Mowgli that's cat-speak for, "Back off, buddy!" My little Mowgli-monster likes to nip after the alarm clock goes off to get me out of bed faster, and sometimes when we're playing, he nips. But a quick hiss and he settles. (It also works when he's trying to steal my supper.)

Oh, yes! And like Catnapper says... Go for another kitten so Pixel can redirect some of his kittenish aggression!