Kenny naturally resurrects after 1-2 turns whenever he dies, and 2 of his 3 abilities kill him if you don't hit the button prompts effectively enough, so this is very easy to farm. If you are going for all achievements on one playthrough, note that this does not automatically void the "No Kid Left Behind" achievement. As long as Kenny is alive at the end of the battle, his deaths will still count toward "You Bastards!" while leaving the door open for "No Kid Left Behind."