Suicidal Murder
 

He was talking to her about suicide, wondering if anyone would really miss them afterwards.
"You know", she said. "Carbon monoxide poisoning isn't so bad after all. You know, staying in the garage with my car, letting the engine run as I slowly inhale its deadly exhaust vapours... After all, in such an enclosed environment, not enough oxygen to create the normally harmless carbon dioxide would exist."
He shook his head for a moment. "But wouldn't it be lonely to die by yourself in this gray, empty place? Can't you bring a friend in to watch or something?"
"Of course", she replied. "But I assume my friend would have to wear my scuba gear with an oxygen tank to survive the process herself?"
Once again, the pale guy shooked his head. "I wonder what would happen if you opened the back door a little so the deadly gases would sneak out slowly instead, and allow you to survive, while you fill your friend's oxygen tank with carbon monoxide instead? You'd get the pleasure to watch her die instead."
The laughed together, both thinking about how dangerously right he really was. Their suicidal thoughts had been swept away for a moment.

wow that is delightfully twisted. makes you wonder