What's the matter, Batman? No witty comeback? No threat? Then I'll provide the narration... 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. But all too soon, the serums and the shocks took their toll, and the dear lad 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. Oh, what the heck, I'll laugh anyway. HA HA HA HA HA HAA!
~ Joker on how he tortured Robin until he went insane
Villains who drive people insane either through contact, sight, or concentrated effort, mind-breakers may do so out for evil ends or they may have it as an active trait. Many villains cause insanity if seen by other characters, some evil hypnotists/psychics drive people insane for fun, and other villains torture a person into madness.