Hmmmm. I don't really focus on funniest joke to like crack at a party, so much as making jokes about the absurd incongruencies I see and experience. That being said, off the top of my head, I have one that still cracks me up:

Two friends meet up at a bar. One friend notices the other is despondent and won't tell him why, so he decides to just keep ordering shots for both of them until he's drunk enough to open up. Finally, after enough liquor has been consumed to sink a battleship, he turns to his friend and asks,

"So what the fuck has got you so down?"

His friend turns to him, wipes away the tears from his eyes and says,

"It's your wife. She's been cheating on us."