NO.  To all of this.  Just no.

Your DH needs to put a stop to this behavior immediately.  And no, his son's behavior isn't normal.  It sounds like he resents you and is taking shots at you to try to make you feel like sh&t.  And tormenting the cat?  It sounds like this kid has some serious issues.  I would absolutely hold DH accountable.  He needs to set some expectations and consequences for his son's behavior.  His son's behavior is disrespectful and wildly inappropriate. 

I 100% agree with Stepmomnorth's post above.  It's time for some conversation and serious changes.

And I am editing my reply to add that the bigger issue is that your DH makes excuses for his son's behavior.  This won't change, at least, that wasn't my experience.  Read my posts please.  My ex SS wasn't nearly as bad as yours, but he was a total failure to launch, loser lazy pothead, quietly passive-aggressive towards me and his dad made every excuse for him and his behavior.  I left my situation for a myriad of reasons, but mainly, my ex refused to parent his kid.  Get out now while you can.  Run.  This WILL get worse.  And I'd be willing to bet that this kid will refuse to launch and daddy won't make him. 

About to throw his cup of water at you, i would have dared him to so i could report him to police for assault and actually act on that if he decided to push it.

its also your partner/husbands job to handle his kid. He is not to talk this way disrespectfully.

my eldest sd would always answer back regarding the parenting of our 2 minor kids who were 1 & 2.5 after meeting them 2-3 times. She actually believed she had that authority and if she dared answer me back whilst hubby was driving, she would get a long drawn out NOOOOOOOOOOO!!

hubby would hear that and instantly tell her off to listen to me. If i say no thats it!! It took him another 1.5 yrs to finally have the courage to sit her down and tell her off that she is his daughter, not his wife, not the mother of our 2 kids and she needs to remember she comes way down the pecking/authority ladder.

hubby also made it clear that when i say something that she was to listen. That there was no answering back, there is no but my mummy and stepdaddy this. 
 

i have not had any contact with sd's since late 2018, they do not come on any holidays with us. The moment my husband told me eldest sd who was about 23 called hubby fake crying on the phone guilting him for marrying me and having 2 young kids with me and therefore abandoning them when they had cut off contact over a year prior to me meeting my husband and it was 5.5 yrs they disappeared with no contact, i wanted nothing to do with them. They showed their true colours then and i was not gonna put myself in a situation where they had access to destroying our marriage and family harmony.

my husband manages his relationship with them away from us. We don't deal or are forced to be exposed to their toxic narcissism 

Exactly WHY do you tolerate this?? My response would have been, "No, you're the lucky one. Throw anything at me and I'll file charges against you. And the next time you are stupid enough to threaten me, you won't step foot back in this house." 
 

As for your DH, WTF??? I know my DH has his faults but he'd never let any of his kids threaten physical violence against me. I'm with StepMomNorth. Your DH needs to step up and be a man. I'd seriously be re-considering this relationship. Wow. 

His son is learning how to be an abuser!  Seriously!  This is BAD. You need to really tell it to your DH straight up and I wouldn't tolerate my animal or myself being around someone who is not only aggressive and a mentally abusive right now but is ramping up to be physically abusive too. 

What's wrong with your husband?  Why in the world is he allowing his brat to treat his wife with such disrespect?  The problem is more with your husband and his failure to correct and discipline his son than it is with the child.  Tell your husband he needs to get his kid under control because you are not going to tolerate it anymore.

It doesn't matter if he is mentally unstable or a brat, the behavior is wrong. Your DH needs to stop the behavior by actually parenting his kid and then getting him mental help if that is what he needs. And you need to tell your DH you will not be treated this way by a child and DH needs to step up or he can find another place to live when SS visits.

day.... then he would rue it more once I got done with what was left after my bride destroyed. him.

Quit tolerating his crap and go immediate zero tolerance on his toxic ass. 

"Children do not get an opinion in this house unless you are specifically asked and as a toxic ill behaved shit, STFU until you are told to speak. If you ever threaten me again, get ready for pain and to be frog marched out of here in hand cuffs by law enforcement.  If  you force that outcome  you will NEVER return to this home. I don't give a shit if I am married to  your father."

Then turn to your ball-less wonder of a non man, failed father and failed DH and tell him to get his failed family shit kid under control or they are both out.

Grrrrrr!

I am so angry for you.

DEAL WITH THIS NOW!

And... who cares if he has a screw loose?  At this point that is little more than an excuse and ja way for others to facilitate his toxic shit behavior.  Destroy it and make sure it never returns to your home and life. Regardless of who its father is.

If he doesn't want to follow your rules than he can move out. Plan and simple. Rather that's with grandparents, mom, whomever. Move out. There's not much light at the end of that tunnel. 

I've just read over your past posts ... Your husband is a disney dad and believes his son can do no wrong and is willing to give him whatever he wants whenever he wants it. Your SS causes trouble in school to quite an extent. His mother has had him diagnosed with a selection of mental issues. This kid is not going to get any better, will probably get worse, and his father has never and will never lift a finger to discipline him. Why waste your life on stuff like this?

Last year, you said you'd had enough and were planning to leave. What happened to your intentions? Life is too short to live in conditions like this ...

Either Dad needs to make some changes or you leave.  There is no other option.  He is putting his son above you and they both know it.  Of course SS is going to make your life miserable.  Because he can.  Because he knows that Daddy won't do a thing about it.  

I don't think you are safe there.  You deserve to feel safe in your own home.  If they won't change, then you make changes.  Get out of there.