I'm with Janna (although I AM a Ross Greene fan - but I accept he's not everybody's cup of tea). If it's something you can enforce, I would turn off the TV program which is producing the "verbal garbage". If he wants it back on, he has to keep those words at bay. If he can't, then the program stays off. And yes, this DOES fit with Ross Greene, in that YOU are now helping him learn self-control - this is not punishment. All you are doing is removing the stimulus that sets his mouth off.
I don't react personally to words like this, apart from maybe saying that talking like that is not going to get any positive results. If the words are directly attacking me, I don't react at all, but I DO store them up for when he's next being nice. If I think he can handle it, THEN I remind him that yesterday he said something unkind which I know he didn't mean. You do need to know what you can get away with, to avoid a meltdown when you discuss this, but if you can do it without meltdown you are likely to have something 'stick' in that brain, at least in terms of words being very hard to un-say.
It's usually difficult child 3 these days and lately he's been pretty good, but when he used to rage A LOT then punishing him while raging did absolutely nothing. He just raged all the more. What I needed to do was find a way to shut it off at the source, and THEN deal with it.
My best example with him is from when he was in mainstream. One evening he was screaming how much he hated me. Probably because I was making him go to bed. He was tired, he'd had a bad day at school, he was simply not able to control himself. Other than replying, "Well, that's a shame because I happen to love you," I ignored it completely and kept him moving towards bed. I knew sleep would be the cure.
Next morning as I dropped him off at school he gave me a hug and said, "I love you, mum." It may have been partly prompted by me saying, "I love you," to him, but when he said that I replied with, "Then why did you say 'I hate you' last night? It wasn't very kind, was it?"
He replied that he had been angry, I gave him another hug, he apologised and we parted as friends.
I'm not suggesting you try this exactly; it works this way for difficult child 3 at least partly because of who and what he is. We also had to work up to this. But he learned to say "I love you" because his grandma kept saying it to him, every time she saw him. And one day he said it back - to her. She was the first to hear these words from him.
I've made a point to distinguish between the behaviour and t he person. I love my kids. I don't always love what they do, but I always love them. I learned from grandma you have to keep telling them this because otherwise they don't think about it or they forget.
I would also talk to the therapist about this, see if there are any suggestions they can make about strategies to deal with this. I do agree, it needs to be stopped. Nipped in the bud.
Marg