My heart melts a little every time Finn calls Ice King ‘Simon’. Finn usually calls him ‘Ice King’, especially when Ice King’s being a nuisance or just, well, acting like Ice King. But when Finn’s more gentle or sympathetic to him, he’ll call him ‘Simon’. Of course, it doesn’t matter to Ice King because that name doesn’t mean anything to him, but it’s Finn’s little way of connecting with Simon, to connect with the part of him that’s still human.