No clue, but all my daughter does is cry to get up and then pound my chest or try to get into the cradle hold. My problem is that she'll try to push my shirt way up when we NIP - my own fault, because I usually nurse at home where I could care less where my shirt goes!
If he's just reaching down your shirt, that's normal. Pinching, I would treat like biting - no nursies when you bite OR pinch. Ba ba? So what? If a toddler can say he wants ba ba for a bottle, then he should be allowed to say it for boobies. I say nummies/nursie, because I read in a Dr Sears book a totally CUTE story about a two year old who got upset and climbed into mommy's lap and said "nursey bout it" and I SO want Hypatia to say that one day! (She's only 13 months so far, but I'm hoping.)