Months ago, DS started pinching me quite hard from time to time, usually when I try and do something like change his nappy when he would prefer to play. I do the 'big eyes' thing and say 'stop, we don't pinch' and firmly remove his hand and then carry on as normal.
Recently, he has started pinching himself in reaction to my admonishment, and now he pinches himself whenever I am even slightly firm with him about something. I realise that he's trying to understand why things aren't allowed by doing it to himself, but is this normal?! I react by gently taking his hand away and saying 'we don't pinch'. It's just a bit strange to see him deliberately hurting himself.