Hmm yeah that could be an issue. Really throwing out other people's things is the main problem here I'd say. Of course it might not necessarily be intentional. If he wasn't aware they were expensive sponges maybe he figured they were disposable. I mean personally I've not used sponges for dishwashing that were not disposable. Now if you had already mentioned it to him, then he's just being an ass about it.
That's usually the issue - he's used to having everything around be disposable, so he throws them out because he's never heard of someone doing otherwise. And it's complicated by the fact that I make the equivalent of about $6 per hour. Money is not something freely available around here.
Hail to the Lord of Death and Destruction! CATNIP FOR THE CAT GOD! YARN FOR THE YARN THRONE! MILK FOR THE MILK BOWL!