Explain that suicide might cause them to miss out on a Utopian Singularity.
Don't. Unless they are already Singularitarians. You'll just come across as weird.
MoreOn: I have no idea what you might say, but unless you are close to both of them and know their circumstances well, I don't see how you could help. (I'll be watching the thread to see what others have to say.) How out-of-the-blue offers of advice or help from near-strangers are taken will depend a lot on their current mood and unless you can accurately read that I'm not sure you would be doing much good. Of course grab all chances that present naturally to be nice and supportive to them, maybe motivate common friends who are close to them to talk to them etc.
Last month, two people far at the periphery of my social circles have threatened suicide. Seems like a sign for me to learn some ledge-fu.
I reviewed the stuff I'd learned back in high school ("Listen." "Be supportive." "Don't argue." "Etc etc etc.") I have trouble believing that this would work outside of movieland, especially on strangers. More so, in person I'm an awkward, fidgeting introvert---the impact of everything I say is thus diminished, and I sound very insincere or clinical, like I'm following a bad movie script, when I say anything like, "You are not alone in this. I’m here for you." or "How can I best support you right now?" I doubt that this would sound any better in writing.
I suppose I could split my question into two related ones: what would you say to a person threatening to commit suicide, 1. in person, and 2. in an email?
I'm looking for out-of-the-box ideas that don't rely on charisma or compassion shining through. Personally, if I ever need to talk myself out of suicidal thoughts, I apply the "bum comparison principle": if my life is so crummy that I'm willing to commit suicide, then I should be willing to just walk out on everything I value and drift off in a random direction, survive by dine-and-dashing out of cheap restaurants and wash dishes if I get caught, maybe take odd jobs or hitchhike or gather roots and berries or blog from public libraries. I don't see this possibility in a negative light, and yet I still haven't done it. To me, it means that however bad my life may seem, I'm still too attached to it to walk out; therefore, suicide isn't on the menu.
People have different reasons to want suicide, and I understand that what works for me with my first world problems probably won't work for a person who is in too much physical pain from an incurable disease. To the best of my knowledge, the two people I mentioned earlier are both unskilled laborers who had lost their jobs, one of them so long ago that he's no longer eligible for unemployment benefits. I don't think I'll meet these particular people again, but I'd appreciate everyone's thoughts on what I could've said if my brain hadn't frozen.