If someone told you he would be going to commit suicide...

[ezodisy]

Mahler: Das Lied von der Erde.

No, I'm serious.  Anyone who's really suicidal won't respond to any "happy" music;

I haven't done any research like Cato but my gut feeling tells me that this is quite obvious. Strauss' Metamorphosen might do the trick too.

[matti]

Better yet, start Der Ring des Nibelungen.

Bull's eye. That'll do the job if the Mahler symphonies did not work. Death by boredom, legal euthanasia, a job well done...