7. A Clockwork Orange (1971)
The Ending... Having been the subject of a controversial new treatment that proposes to "cure" him of his violent, murderous ways, Alex DeLarge finds himself driven somewhat mad in the process, and eventually winds up injured in hospital. When the government suspect that the media will take the story and blame them for the experimental failure, Alex agrees to cooperate and make them look good. In exchange, they'll let him be himself again.
The movie ends with Alex commenting, "I was cured all right," whilst imagining himself having gratuitous sex in a public space.
What Everybody Thinks... "Oh, so, he's... cured, then?"
But Wait... Alex's comment about being "cured" has given rise to a number of misinterpretations regarding the end of A Clockwork Orange, and that's because lots of people fail to pick up that he's being completely and utterly sarcastic. He's only "cured" in the sense that he's back to his old self, hence the sex sequences that flashes up as he utters this comment.
The fact that the UK version of the book has a completely different ending (Alex is genuinely cured, in that he gives up being violent of his own free will) hasn't helped matters with regards to this one, though.