I expected him to just break off a piece of it, but nope, he just dented it to hell. God what a moron. His lack of boundaries with women (no mother or female friends), and lack of understanding of money, I can understand.
But selling someone else's possession (granted, the princess DID say they didn't need it, but she also didn't say to sell it), and when told it is too valuable to sell, just destroying it? Come on.