Bunny,
I can relate to what you're saying. It rots big-time! For many years I was referred to as every nasty thing you can possibly think of and more by my difficult children. I was told by difficult children's therapist, psychiatrist, to remain neutral. Ignore what I could. This didn't work and left me wanting to scream, punch holes in walls just like they did. When I felt this out of control, I usually went for a run. This calmed me down enough to deal with the next nasty comment that would fly out of one of their mouths. However, there were those times I'm not proud of when my emotions got the better of me and I would yell back. This only escalated the situation to the point that sometimes I would have to either call husband to come home or lock myself in my room.
I had to learn the hard way that the only way to diffuse the situation was to remain calm. However, I didn't have to take all the "garbage" spewing out of their mouths without letting them know how inappropriate it was. Once the tantrum passed, I would tell them in as few words as possible, another suggestion made by difficult children's therapist, why this sort of behavior is inappropriate and will not be tolerated. There were negative consequences for their outbursts. Unfortunately the negative consequences usually resulted in another meltdown. Eventually, I learned to go with natural consequences whenever possible. If they called me a F*ckinB*tch, one of their favorite terms of endearment, to borrow an expression from a long time member, then half an hour later wanted something from me, I could let them know that after being called an FB, I wasn't in the mood to spend time with them, etc...
Wish I could say this helped but in reality it did little to stop the steady stream of "garbage" coming out of their mouths. Sad to say, I think the only thing that made a difference was time and distance between us. Once they were no longer living in my house, things improved dramatically. I think lots has to do with the fact that as another long time member used to always say, they weren't finished cooking. Unfortunately our difficult children mature lots slower than typically developing kids and have much shorter fuses.
Wish I had some advice that would actually help you. Just want you to know I'm thinking of you... Hugs... SFR