Was invited to my sister's for Mothers Day, along with my mother and my 2DC.
Everything was lovely, food was lovely, mother got lots of lovely presents.
After the lovely lunch, just as everyone was relaxing watching tv chatting, I asked my eldest DC to take my mug into the kitchen since he was already going that way. He refused, so in a jokey way, I said 'Oooh, I'll have to think of a suitable punishment for when you get home.'
My niece (7yrs) suggested I could make DS do some cleaning. 
DS visibly tensed at this, and explained to niece that he 'already does some cleaning and only because he has to, so your suggestion is so not funny.'
Niece then whispers very loudly that I should throw DS out in the cold for one night.
I said I didn't think DS would like this, at which point DS said to me 'You just try it, just try it once and see what happens!!' 
I said 'That's enough, stop being silly DS, it's just a bit of banter.'
At this point, my nephew strides into the room, turns directly to me and says 'I'm sick of hearing you and DS arguing in my house every couple of months, and if you hadn't noticed, that lady in the garden is your MOTHER and if you also hadn't noticed, it is Mothers Day, so I suggest you either shut up right now or leave the house, because I don't want to hear your arguing anymore.'
I stood up and said I'd leave then. 
DS refused to leave with me, so left him there.
I am speechless, shocked and don't know what to do next.
Perhaps I should mention that nephew is 16, DS is 19 and I am almost 40, and I have issue with a 16 year old speaking to me so aggressively and being humiliated in front of DS, and other younger nephews.
DS and I have a difficult relationship because DS contributes very little in the way of time/effort/financially towards our home, argues about being given any small jobs to do, and pulls a murderous face every single time he is asked to do anything. DS has very little respect for me or his sister, if any at all.
WWYD in this situation? AIBU to be pissed off at being spoken to this way by my nephew? And if IANBU, What can I do to prevent it happening again?
Starting to feel like no one has any respect for me.