The inimitable Patton Oswalt stars as the Penguin in this laugh-out-loud (I mean that in a literal way, not in a "standard adjective for funny" way; I laughed out loud while watching it) video from College Humor that co-stars fellow comedian Pete Holmes as the Caped Crusader.
In the video, the Penguin and Commissioner Gordon good-naturedly but futilely attempt to explain to Batman that his "one rule" — that he will not kill people — has actually been broken several times, before ultimately realizing that Batman has no actual grasp of the concept of death. Batman gruesomely kills multiple criminals mid-conversation without realizing that they are dead and not "asleep," which astounds both Gordon and the Penguin. Then things take a turn for the ultra-violent.
I'll stop explaining the joke of the video and let you just watch it yourself, but before you do, understand that after watching it, you're going to want to watch all three Christopher Nolan-directed "Batman" movies and count how many criminals Bruce Wayne actually kills.*
*I counted — it's 278.**
**Just kidding. Ain't nobody got time for that.