I would be so tempted to write back something like, "You deserve to live free of that kind of anger. If my website makes you that upset, please stop looking at it. I suggest incinerating your computer and stapling your eyes shut to ensure that it never happens again. Life is too short for anything else."

That would probably only bait the troll into doing something worse, though.

I wonder if it would be helpful/cathartic to have a central repository of hate mail that everyone could share their "fan" letters to.