And why are some DHs such brats?  Doesn't he reprimand his son's rudeness to you?   If not he's a knobhead, just like my DH used to be when he never got on the case of my SDs treating me poorly.  Because we're expendable, I suppose, and the snowflakes are not. 

Sorry I cant answer the why portion as I have to shake my head at some of these kids and parents that I come into contact with in public on a regular basis, however although I had highly disengaged from my exes kids when they were younger, I would still not put up with being disrespected or rude behavior in the home and I didnt even live there full time!

If he is young enough, or at least smaller than you, LOL, I would very clearly yell at him myself.  I had to do that when my exes kid was younger.  He would try to interrupt me and my BFs conversations at times and I wont stand for that, so I made it known right then and there and looking him straight in the eye that you DO NOT interrupt adults when they are speaking!  The reason I state that if they are smaller than you or younger is because when the tantrums start or the melt downs, you either immediately direct them to their room, or if they refuse to go, you take their hand/arm and direct them there!  I had to even do that with my daughter when she was little.  She was made very much aware that you can have all the tantrums or pouting fits that you want, but it will be in your room behind closed doors, not in the common areas of the house to annoy others and just for attention only.   When you have decided to act like a human being then you can come out.

Now if you are completely disengaged or dont wnat to do it yourself, you demand that DH does it and Im not talking about later or after the fact, I'm talking about right then and there!  The kid interrupts your conversation, you stop mid sentence, state to DH that he needs to take care of this rude behavior and I'll resume our conversation once that is done.  Same for tantrums, if the kid tries it, you demand that DH deal with it and remove the kid from the room that you are in immediately.   STAND UP for yourself and demand that you are treated with respect in your own home!

Because their fathers are so afraid of losing custody and having to pay more money to their BM that they get themselves as far up their children's rainbow spouting asses as possible. BMS and skids both demand that bio dad's pay them tribute and avoid upsetting them in any possible way because they hold the cards, or so they think. These indulgent dad's not realize that there's another way to do it which is gross and fucking balls and fight for their rightful custody rather than begging for scraps from BM. 

When I explain it that way to my husband he realize how much of a wimp he was being and how unsexy I found it. That got him in shape pretty quickly. But that is mostly because he cares what I think. If you have an SO that doesn't care when you tell him how unsexy it is for his ex-wife to carry his balls in her purse then you have a problem because that means he cares more about beings opinion than yours.

He lets SS control your home. You don't like haveing SS in control.  Time to talk with DH. He has to step up and be a parent. 

Because their parents don't parent them. My SS would have regretted opening his mouth if he ever insulted me, because DH would have dropped the hammer on him.  The real question for me is: How do their wives respect these men who allow their children to be such brats?

Give him a dose if his own medicine. I started being rude and passive aggressive with SD and finally she has stopped being a brat.