It's natural rabbit behavior. Mine will scratch me when they want me to do something. He's not being mean, he wants your attention and it's his way of saying hey do what I say!
Push his head down (very gently of course) when he nips you and make a high pitched squeal. This is what mama rabbits do when they are disciplining their young. I did it with Shirley when she had cage aggression and it worked pretty well.
Boomer does it... i call it 'digging to china' usually through my shirt on my chest or my arm... he will bite holes in my clothes if i let him chew them. it's all for attention.
Gandalf does this for attention too. It's half way between sweet and painful. He learned quickly not to nibble me or my clothes so now he will dig on my leg then lick and nibble the sofa cushion next to me hwell: