Joffrey is at the Small Council meeting, for a change. He's standing up, because they still have that chair situation going on. And because he's positively giddy, so he can't sit still. Pycelle starts to give a note to Tyrion, but he drops it so Tyrion has to reach for it. It's a pretty feeble move by Pycelle, but I guess you use the tools available to you. The message reads, "Roslin caught a fine fat trout. Her brothers gave her a pair of wolf pelts for her wedding. Signed, Walder Frey." This is too heavy on the animal metaphors for Tyrion, so Joffrey explicates: "Robb Stark is dead. And his bitch mother!" And he's going to serve Robb's head to Sansa at his wedding. Tyrion bristles at this, as you might imagine. Cersei says it's a joke, but Joffrey says it isn't. Tyrion is of the belief that since Sansa is no longer Joffrey's fiancée, she's no longer an option for him to torment. Joffrey says, "Everyone is mine to torment." This is his idea of the droit du seigneur, I guess. He also drops a line about Tyrion being a monster, which is just a setup for Tyrion to say, "Monsters are dangerous. And just now, kings are dying like flies." Joffrey stares at him, shocked. As though it's the first time Tyrion threatened to kill him. Then he looks to Tywin, who's just watching the whole nonsense. Finally, Joffrey sputters, "I could have your tongue out for saying that." Cersei tries to jolly Joffrey along, saying that Tyrion's a bitter little man who should just be ignored. It looks like he's going to be momentarily mollified, but then Pycelle takes Joffrey's side, saying Tyrion should apologize. Joffrey pulls his hand away from Cersei and insists, "I am the king!"
At this, Tywin finally interjects, "Any man who has to say 'I am the king," is no true king. I'll make sure you understand that when I've won your war for you." Tywin has no interest in coddling Joffrey anymore. And as a result, Joffrey insists that his daddy (Robert Baratheon, not Jaime) won the war against the Mad King while Tywin hid at Casterly Rock. There's quite a pause. Tywin says, flatly, "The king is tired. See him to his chambers." Joffrey quietly protests, but he lets Cersei lead him away. Tywin suggests some essence of nightshade to help the king sleep. Joffrey shouts, "I'm not! Tired!" But off he goes. And so does Pycelle, who takes along the note from Walder Frey. That's good thinking; you don't want that sort of thing lying around. Save it until you need to blackmail someone with proof they were in on the scheme.