gun

fire

poison

knocked off a bldg

ect

He smashes Jokers head through the Batsignal.

Outlives him!!!

Throws him in a ring with Brock Lesnar.

With a crowbar

I actually can't imagine one.

Beata

Beat him with crowbar almost to the death. Then kill him with explosion and later revive him with Lazarus pit. Then shot him with gun in stomach, to broke his spine... shot him again in upper right arm... And finally shot him in the head. To be sure that he die... cremate his body :D

Or just broke his legs and hands and leave him in some cell to die of hunger, to be sure that he will die leave him starved Athony Romulus...

Or just hang him upside down in some cave, cut his neck just a bit to he bleed slowly... slowly to death... To be sure that he will die, hang him in Man-Bat cave...

Or just spill liquid nitrogen on his arms and legs, use mallet and smash legs and arms... then throw him in cell with starved Killer Croc...

Or just... idk whatever i already mention... he earn anything of that !!!

Lets the cave drop on both of them after a gruesome fight convincing Joker he is sure Joker wont die because he is a demon and not a man.

With a killing joke ;)

Batman is not killing the Joker..