DS is 19 months and is a shocking hair puller. He mainly only does it to me, he just grabs handfuls of hair and wrenches (often when he's over tired or over excited). I have tried calmly asking him to let go, I've tried acting really upset and putting on a sad face and I've even lost it and yelled - he just thinks it's funny and keeps doing it. I demonstrate to him what 'gentle' is by stroking his hair or check and he copies that, then goes in for another pull. How do I get him to stop and realise it hurts??