Something about insanity has always appealed to me. If I tossed in a disclaimer saying, "Not that I'd really want to be insane or anything" I'd be lying twice over. For one thing, I do kind of want to know what it's like. And secondly, as it is I'm already quite aware that I'm a little bit what you might call 'strange in the brain'.
That or, as I suspect, I'm just more honest to myself about my thoughts and motivations than most people.
I love listening to BioShock splicer dialogue. It's just so good and creepy. Grossman, sorry, Dr. Grossman's is my favorite. Just listen to that maniacal laughter @2:02.
Which should remind you of the Joker, specifically the one voiced by the wonderful Mark Hamill.