You're gonna die anyway, why hurry it.
This. I don't understand why anyone thinks this helps.
I think everyone got most of them down, but I'll add some.
"If you can't live for yourself, live for me. I'll be sad if you die."
"If nothing matters, then everything matters. It's just your perspective." (or any variation of spinning nihilism into a positive light)
"That's just life. Suicide is never the answer."
"People who are suicidal are incapable of rationally deciding to end their lives."
Note: I do think most of these phrases (not just mine) come from good intentions, but that doesn't make them any less unhelpful.