First off, He's an 18 y.o. kid.
You have to get his attention first.
Your calm, good natured lecture made his eyes glaze over.
Maybe something like, "You're an IDIOT!"
"How are you ever gonna get laid again if you KILL yourself?" might work. But probably not.
He has to have his "I'm not Immortal?" moment all by himself.
Hopefully he'll live through it.
I almost didn't.