Season 8, episode 22: "Everybody Dies".
Everyone didn't die. Disappointing.
Warning: Spoilers below.
Seriously though, what a stupid, mawkish way to finish the show. I really was hoping that somehow everyone would die. Or at least that House would. It looked like they were at least going to deliver on that, with his whole life collapsing and him just deciding to kill himself.
And I even held out some hope that when he had his epiphany and decided that he could change that he was going to just be killed before he could do anything about it, but then they copped out of doing that too.
And during the funeral scene with everyone talking about how great he was, I really hoped that was just him imagining that and that it would cut back to him dying in the fire and then show his actual funeral where either no one or just Wilson showed up.
But no, he fakes his death and doesn't have to go to jail and everyone gets a happy ending. What a letdown.