The Joker's Greatest Crime!

Arguably, the Joker is one of the greatest villains in all of comicdom. Why? Because he actually causes lasting physical and emotional damage to the hero. The Clown Prince of Crime has single-handedly killed both Robin (the Jason Todd version), crippled Batgirl, and been a thorn in Batman's side for a handful of decades. But, what was his worst crime, you ask? Perhaps poisoning the cosmetics in Tim Burton's film version? Ruining Harvey Dent's life and destabilizing Gotham in The Dark Knight? Maybe the time he overthrew Arkham Asylum, nah...it's all child's play compared to the shocking events in this panel from a Batman coloring book: