Do you cuss AT your kids?

Tonight I was over at my aunts house for dinner; (I mostly go over to see my baby cousin) she had her 2 year old grandson, daughter, son and daughter in law over. My little cousin has autism and associated with that is behavior, and communication issues (he is learning signing atm). I was sitting on the couch watching him play on the floor with Lincoln logs, just minding his own business; he gets up and goes to the fridge and starts signing for some milk (he is a very picky eater and drinker) I point out he is thirsty and they weren’t pay attention to me, I went to get up to get him some and he starts banging his head against it.

My cousin (his mom) grabs him and he has an episode, thrashing around, yelling, hitting etc! She yells “you’re such an asshole”... my aunts stands by and says “yea you’re such an asshole sometimes”.

At this moment I’m at an awe, I said “why are you cussing at him like that? You guys know his signs of a future episode, he’s not an asshole. He tried to tell you something and you weren’t looking”. She asks me “what’s the big deal anyways? people cuss at their kids all the time, they don’t know!”

I think my aunt and cousin were wrong for cussing at him like that, plus they have cussed before not at him but just if he is climbing on something or throwing something he’s an asshole for it... they don’t hit him or abuse him physically it’s just the verbal cussing but other than that I know they love him he is spoiled rotten.

Do you cuss AT your kids? Do you think it is ok too cuss AT kids? Should I have done more than just speak up?