In case you are wondering what is going on, let me tell you a summary of it. Ben Affleck is Matt Damon's best friend. Matt Damon is Jimmy Kimmel's friend and Sarah Silverman is Jimmy's girlfriend.
At the end of every show, Jimmy will always poke fun at Matt Damon. So, one day Sarah Silverman and Matt Damon team up to sing a song call, I'm Fucking Matt Damon.
Out for revenge, Jimmy teamed up with Ben Affleck and a couple of other celebrities to sing a song call, I'm fucking Ben Affleck.