Some friends have DC who are really difficult in terms of behaviour recently. The Dc are young and I was quite chocked as they were saying things like "Mummy's stupid, mummy shut up'. Thing is the dad sometimes speaks like this to the mum. Kind of jokingly, as in 'Shut up' said in a sarcastic kind of way..
Anyway I wondered if maybe the source of this is from copying the dad and way he is to mum.