Hi B.,
My one and amost a half year old daughter is also usually very well behaved. She also just began exhibiting similar behavior. She is into the pinching/hair pulling thing. When she wants something and can't communicate it she gets frusterated. I've also noticed that she does this when she gets excited as well (which is usually just another form of communication frustration...I can't expect her to automatically know how to express herself...verbally or emotionally this is mostly learned). I can tell you that when she does this I say no and correct her showing her how to have fun, play, etc. nicely. I f she continues I leave her to sit away from me (and my hair!) until she calms down and is ready to play nicely again. I know it's frustrating, but from what I hear it's normal and one of the many "fun" phases we have to look forward to!
Another quick thought: if he is in daycare like my daughter, he may be picking up things like this from watching other children. They all have their own little ways about them and how they deal with expressing themselves....i.e. pinchin, hitting, pulling hair, etc.