Titan Joker from Batman: Arkham Asylum. Seriously. You'd think a boss that looked like a cross between The Joker and The Incredible Hulk would pack more of a wallop. He hits hard, yeah, but all you have to do is avoid him, and after maybe two seconds of cat-and-mouse, he'll lose interest in you for some reason and start mugging for the police chopper, at which point you can fire the Batclaw into his back and drag him down for a cheap hit.
The only aspect of the fight that could be considered even remotely challenging would be taking out the waves of thugs he sends out at you quickly and with as little damage as possible, and at that point in the game, the player shouldn't have any trouble doing it.
What the hell, man?