Ds1 (4yrs 7mo) at times when he is stressed, which can last weeks, hits, punches, spits at, kicks ds2 (2yrs 9mo). Ds1 not dx but anyone who spends more than an hour with him can see he is some level of ASD (excpet HV or Paed). If he's not physically hitting him he will shout, pull faces, and his favourite is to sing stupid hurtful bullying songs in ds2's face.
Nothing will make him stop. I've talked to him about it and he says he does it because he likes it. I believe this because he loves ds2 and plays with him, defends him, and can be kind towards him.
I have 2 theories - either that he likes the repetition - because he knows the exact pattern of events that will come out of that behaviour - or hearing ds2 cry is a type of stimulation he enjoys.
Any suggestions.