Man, that guy was rude, inviting someone else's vassals over to switch side in front of the lord. Even as a joke it's in pretty poor taste. It's just showing complete lack of respect for him because he's a kid, and he doesn't call him out on it. Instead he's actually deferential to the guy, even though the guy is just a vassal and he is the heir of a territory. I get annoyed by him being so humble all the time. It's one thing to be kind and nice, but you should remember your place at times too, especially when people are walking all over you.