Cameras. Everywhere. 

If anything was thrown at me and hit me.. it would disappear.. forever.

If he asked what would happen if he pushed me in the pool.  I would dead eye look at him and tell him.. I don't think you want to find out bubba.  Just remember.. you have to sleep sometime.  or.. I'm the one that cooks your food.. evil grin.

For the pretend hitting etc.. I would actually just call him out on this.. say.. "are you having a seizure.. do we need to get you evaluated?  

Then do it.  Self defense should be applied as forcefully as necessary to end this bullshit.  Where is the idiot father and why isn't he resolving this resoundingly?  One word of this shit from our mother to our father and it would have been game over for my brothers and I.  Though none of us would ever pull this kind of crap.  We were well raised and well parented. Unlike your DH's failed family breeding refuse.

"Do it and find out you little piece of shit.  You will be gumming your food for the rest of your life because you will eat whatever blunt object is at hand." 

Leech was 16 and kept hitting me with a dogs ball, I got fed up with it and one day when she "Accidently" hit me with a ball in my back. I picked up the ball and told her that I would throw it back to her so she could throw it more for the dogs. What the little witch didn't know was that I grew up around a bunch of boys and could throw a ball hard and fast. Leech thought she was the best at everything and that she could catch the ball. I threw that ball as hard as I could, she missed it and the ball hit her square in the middle of her forehead, I just gave her a smirky grin and said "Oops", that was the last time she ever threw a ball at me.

Next time you SS hits you with a ball, rocket that ball right back at him. Or if he's next to the pool, push his ass in the pool and just say, "Just wanted to see what you will do now, don't dish it out if you can't take it".

As to the faux hitting or stabbing, let him know that what he is doing is threatening and you will defend yourself.

Send the little sh!t to his room, every time.

So he's threatening physical violence to see what you would do? That is not ok! Do not be surprised if when he dates he ends up being physically abusive to his partners. 

I would guess he's thinking he wants to actually hit you, but knows he shouldn't/can't.

Ugh, SD11 is always "just joking" too when she says anything rude/passive aggressive. If DH or I say anything to her, that's her immediate go-to. These SKs are in fact NOT joking, just an excuse they use for their behavior *eyeroll* I just flat out tell her, "Well, you're not funny." That shut her up real quick with all the "jokes" she was telling. 

Example SD11: "Dinner is soooooo gross. It's so burnt it's crusty!"

Me: If you don't like it don't eat it.

SD: "Geez, I was just joking!" 

So. Annoying.