I don't, well I do ocasionally but I want to go in super nanny style and sort the mess out!
My sister does nothing to disipline him, she has no confidence in herself at all :(
For example at a party recently we were at soft play first, they had go karts.
Her DS (who is 4) drove past on his and in front of the whoe party shouted 'OI fatty' to his mum!! 
she just laughed it off and confessed he does it all the time.
Nothin came of it.
If that were me I would have took him from the kart, sat him down, told him he does NOT call mummy or anyone names like that. Made him sit for 4 mins and apologise.
When we got to the party after at the birthday boys home my nephew followed the birthday round screaming it was 'his turn' for the new toy he had gotten.
my sis kept saying feebly 'its xxs birthday and its his toy'
but my nephew just continued this moaning, screaming behaviour the whole party and it was embaressing.
You could see everyone was thinking 'FFS tell him he is not having it!'
I feel sorry for her, shes in an on/off reltionship with DNs dad, who i know has been abusive in the past ( fatty comments come from somehwere!!
) and she just doesn't seem to have the energy to control him :(
I try to help but she doesn't follow through with any of the disipline advice then says to me 'why are your 3 kids less work and more well behaved than my 1'?¬!