I was at a friend's house last week for a gathering of about 20 people and one couple brought their DS aged either 5 or 6 with them. Whilst they were in the bigger room with the wine and nibbles, their DS came into the smaller room at the back where a few of us were chilling out and chatting.
He started trying to entertain us, as kids do, but imo, he pretty quickly got out of hand. He started by running up and down the corridor between the two rooms and shouting (fine), but then slamming open the door of our room so that it was banging into the wall quite forcibly.
He then started playing with the landline phone that was in our room, even though the host who was there asked him not to. The host doesn't have DCs and was obviously not willing to really discipline someone else's, but eventually he got ticked off and took it off the little boy - who then climbed on his lap, hit him, and started trying to grab it off him 
He also started shouting, 'Be quiet, all of you, SHUSH' to us whilst we were chatting.
AIBU to think for a child of school years this is pretty bad behaviour and the parents really should've intervened? 