Ds (9) poss ASD.
At home he will often make really inappropriate comments about sex, we pull him up every single time, but it is not sinking in and he carries on making comments.
He is not abused (isn't with anyone else alone so I'm 100% sure of this), he does not have access to unsupervised screens, so we know he hasn't seen porn.
His teacher has told me that this has now happened at school occasionally, and rightly they are slightly concerned - he is younger than they would expect to see this behaviour.
We do know that he has probably heard things from his older brother and he had a sleepover with a cousin and was allowed to watch Family Guy and Ted.
How do we tackle this? I had a word with him in the car and he ended up having a meltdown, the teacher is (apparently) a lying bastard (she's not) and is now on his hit list 
Is this normal ASD behaviour? We have never had anything like this with his older siblings. If they've ever said anything inappropriate we've told them and that's been the end of the matter.
Help! :(