The boy king (played by Jack Gleeson) seized the Iron Throne on the HBO drama, killing Ned Stark (Sean Bean), father of Robb (Madden).
"If you disliked him last season, you're going to hate him this season," Madden told Vulture. "He's really messed up."
He added: "I'd love to kill Joffrey. I'd love a Joffrey-Robb standoff. I need to find a way to slit Joffrey's throat. That would be awesome."
Madden also admitted that he enjoyed a Game of Thrones fan video that recut a scene in which Tyrion (Peter Dinklage) slaps Joffrey.
"There's a ten-minute video online of just Joffrey being slapped, over and over again," he laughed. "And that's brilliant. Who doesn't want to slap Joffrey?"
Game of Thrones airs Sundays at 9pm on HBO. It is broadcast in the UK on Mondays at 9pm on Sky Atlantic.
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