I received several *private* answers to this thread and some of them are pretty creepy:
What should I answer to a nice guy who said he will kill himself if I die? For Darwin's sake, already have enough bad karma to my all eventual next lives! :-/
And what to say to another sweet guy who said I can't do this kind of prank because he is very anxious? I didn't know he was anxious and it was only a joke... The world is becoming strange, isn't it? :-/