Bronn refers to the joke "Tywin shits gold", which was first mentioned by Robb in "The Pointy End".
Joffrey says that Brienne killed Renly.
Martin tells Butters and Scott a spoiler - that Joffrey gets poisoned.
Tyrion is accused of Joffrey's murder. Shae repeats the sentence Tyrion told her "I am a whore, remember?".
The decapitated dwarf, that the bounty hunters brought Cersei, was one of the dwarfs who performed at Joffrey's wedding. Sansa says that she saw Brienne at Joffrey's wedding, bowing to him.
Melisandre mentions Joffrey's death.
One of the scenes in the play "The Bloody Hand" features Joffrey's wedding and death.
Bronn offers to train Podrick Payne how to fight dirty, in order to survive in a real fight. He gave similar advice to Jaime on "The Lion and the Rose".
Olenna refers to Joffrey's death.
Arya mentions Joffrey's death.
Jaime and Cersei speak about Joffrey's murder.
Cersei refers to Joffrey's death.
Tyrion and Sansa refer to Joffrey's wedding.
The death of Joffrey Baratheon is #5.
The Purple Wedding is #5.
King Ralph is poisoned by his drink.