DS1 is forever telling his younger brother that he is stupid, silly, etc. Sonetimes it is just constant, a stream of "oh DS2 you are so stupid. No! Stupid DS2! DS2 is stupid! DS2 is stupid!"
Today DS2 was painting and didn't get the colours as he wanted. He said to himself sadly "stupid DS2". This breaks my heart. How can we stop DS1 from being so horrible? He has never heard any of this from us, we have never called him or his brother stupid - we give a lot of praise and positive feedback.
What would you do? I know some jealousy and "you are a poo" type stuff is inevitable but I think this goes beyond that.