I've been muttering the chorus to this song under my breath non-stop for the past several hours...the Joker is my favorite DC super villain and I think you've captured the character perfectly here, which is hard to do for a lot of people. You managed to find the right balance of silly and terrifying, all while making the song catchy and fun to sing along with. I applaud you.
PS: Before reading the thread I was under the impression that you had sampled Mark Hamill's joker laugh for the song, but having been corrected in that I find myself even more impressed. A good Joker laugh is really, really hard to pin down. Trust me, I've been trying for years.