Joker said it best...
The Joker: What's the matter, Batman? No witty comeback? No threat? Then I'll provide the narration...
[the screen flickers to life and "Our Home Movies" appears]
The Joker: I'll begin with how I peeled back the layers of the boy's mind. Oh, he bravely tried to fight it at first. You would've been proud to see him so strong.
[on the screen, the home video of Joker electrocuting Robin appears]
The Joker: But all too soon, the shocks and the serums took their toll, and the boy began to share such secrets with me. Secrets that are mine alone to know... Bruce. It's true, Batsy! I know everything. And kinda like the kid who peeks at his Christmas presents, I must admit, it's sadly anti-climactic. Behind all the sturm and bat-o-rangs, you're just a little boy in a playsuit, crying for mommy and daddy! It'd be funny if it weren't so pathetic.
[pause]
The Joker: Oh, what the heck, I'll laugh anyway. HA HA HA HA HA HAA!