9. Shooting Babs & Kidnapping Jim Gordon (The Killing Joke)
1988's The Killing Joke revolved around the Joker's attempts to drive Commissioner Gordon insane, in order to prove that "one bad day" can make even the most stable and controlled men go mad. The way in which he does this is to shoot his daughter Barbara (Batgirl) and kidnap him, stripping him naked and locking him in the cage of a circus' freak-show, making him view pictures of his injured and naked daughter. Obviously, it goes without saying, these events were far more traumatic for the Gordons than they were to Batman, but the fact is that these were two people dear to the Dark Knight so they obviously traumatised him too. Batman, of course, saved the day and rescued the pair, but Barbara was left crippled and in a wheelchair, which would obviously have resonated with the Dark Knight for some time.