Dress as Charlie Chaplin dressed as Hitler. Problem solved.

But srsly... People dress as satan, demons, the very embodiment of evil. So why would an example of an evil guy be worse? Dunno, but I'm pretty sure it would be. Maybe because there are still people around with relatives he killed, and unlike any one particular serial killer, there's a decent chance you'll run into one.
It wouldn't bother me, especially since he was so goofy looking and ripe for satire, but you might get a few touchy people screaming at you.