this is kind of tough. i think there's a lot of things you could say to either of them to piss them off, but to really break them.... for vanitas, i think he'd have to dig deep into his core and tell him that he's a death omen, that he brings suffering and death to everyone around him, and that he's a coward and a fake for not dying in their stead. for ruthven, i'm less sure. maybe that the world is broken and he'll never be able to fix it, or that he's the pinnacle of all the worst things about humans and vampires. but we don't rly know enough to know exactly how to get under his skin, and that's likely on purpose.