I don't think it's whether you reply or not...I think it's whether you believe the garbage he is saying. If you believe it, you will naturally reply, defend yourself, and completely lose your mind trying. If you remember that whatever is being "thrown" at you, like name calling, is just simply not true then, then it becomes easy to not respond.
Sometimes my response to AH is: Why don't YOU think about that for awhile, and let me know if that's really possible/true.....pause....no reply from AH....and I say "that's what I thought".....
Not saying that's a good answer, but it makes him go quiet for a whole minute sometimes. I guess what I am really learning is how to manipulate him right back. Stupid way to live, but sometimes we just have to do what we have to do.