I have to disagree with Rob and Mike. I had the same situation when I moved in with my GF (now wife of 9 years). I think that when you get to the point in the relationship that you're living together, punishments are up to BOTH adults, not just the biological parent. Yes, respect for other's property should have been taught from day one, but if there hasn't been a male figure in his life consistently then I see where the problem lies. He needs to be taught respect and guided in the right direction.