I definitely understand where you are coming from. Before my son was born, we had the family over for Mother's Day. JD's room was "done" and all of his toys were washed and on the shelves. My neice (6) is a mean kid, no other way to say it. She didn't like that people were excited about a new baby coming, so she threw his things on the floor and stomped on them. She has also deliberately hurt her siblings and is very sassy to adults.
Needless to say, she is no longer welcome in my house unless she can follow our rules. I immediately took her into the den and firmly stated that this behavior would NOT be tolerated in my home and if she couldn't follow those rules, then when the family was over she would need to stay in the den. She yelled at me that I wasn't her mother and I calmly informed her that it was my house. She stayed in there for about 20 minutes before she was ready to be civil.
Her parents give-in to everything and she's mean and bad at home, but not at my house and not in school! Hm... coincidence? Set the rules clearly as well as establishing a clear (and reasonable) consequence. At our home, if she's nasty, she gets a time-out in the other room until I think she's ready to rejoin the group. If she's nasty when we're at my in-laws, we leave.
Bottom line, your child is your priority. She needs to be safe and doesn't need to see him get away with bad behavior.