Like the previous entry regarding the comic book version of the character, Heath Ledgers Joker in The Dark Knight is theorised as actually being aware of the fact that he is a character in a movie. In this case, it's based on the fact that, unlike most versions of The Joker, Ledgers version barely ever laughs. The reason behind this is suggested as being because his audience are those who are watching the movie and, like any good comedian, he knows it's uncouth to laugh at your own jokes in front of people. And then look at the the three different stories he gives to people about his scars. The people he gives those contrasting stories to have no reason to believe that the Joker isn't telling the truth. He achieves absolutely nothing by playing that particular prank on them, so every time he tells a different story the only people who can possibly get the joke are those who are watching the movie. He loves being the centre of attention, but the only people who could possibly give him a reaction - which he clearly wants - are the people watching at home or in movie theatres. This heightened level of self-awareness borders on omniscience and the theory is that it can only be explained by him knowing that hes a movie character. There are also theories that various animated versions of the character know that they're in a cartoon, thanks to breaking the fourth wall and so forth, but three entries of that nature in the list would be pushing it.
