Is it illegal to tell a suicidal person to do the world a favor and just kill themselves? I don’t like asking this question because in my mind it’s very wrong but i’m in a debate about it and i can’t find any answers! 
Crisybelle, welcome to the SDMB. One of the problems with asking “Is it illegal” to do something is that laws vary wildly depending on where you live.
Things like murder, robbery, etc. are generally illegal wherever you go, but for a question like yours, it will probably vary by location.
IANAL, but I know some places have laws against assisted suicide. I don’t know whether a statement like this would fall under those statutes.
There is also the oft-quoted statement that freedom of speech is not absolute, with the example of crying “Fire” in a crowded theater. This seems fairly close to the situation you ask about.
In short, I don’t think this is a question with a yes or no answer. You may have to be content with “It depends.”
I asked a shrink about it one time.
He said you have no responsibility for a suicide if you don’t physically assist.
It would be a better cite if it had been a criminal defense attorney or district attorney than a shrink…
IANAL and I’ve never played one on TV. We really need a lawyer to comment on this. Meanwhile Wikipedia says:
But is suicide a crime? Again Wikipedia:
That’s murky enough that I’m not sure if suicide is legal or not. 
Also there is a concept of “disturbing the peace” which seems to mean “anything that police officers don’t like”. And they would not like it if you were yelling “Jump!” at a potential suicide standing on a ledge. You might get arrested on that basis.
Yeah, that sounds like a safe and sure way to get a ride on a patrol car. There are cases more subtle though. If someone is despondent and you have their ear and you support their idea that life is not worth living, that’s the kind of stuff that his loved ones might want to prosecute.
I used to volunteer at a crisis intervention hotline, and we had our share of suicide calls. I have to admit that once in a while we’d get a call from someone whose life was so totally fucked up, that we’d be tempted to say, “Damn, if I were you, I’d already have slashed my wrists.” I’m sure that if I had done that, and other people found out, there’d be the risk of a huge law suit by the person’s family. And my work at the hotline would definitely be over.
But I don’t believe it’d be actually illegal.
Yeah, we have criminal law here and we have civil law.
So far the consensus seems to be that suggesting suicide won’t leave to criminal prosecution.
The issue of civil suit is a separate issue.
It appears you CAN get sued for someone else’s suicide. Witness media figure Nancy Grace being sued for allegedly causing the suicide of a guest on a television show.
Now, can you get a conviction? I couldn’t dig that up.
This being said, 99% of conversations are not taped. If you told your buddy Jim he should off himself while you were hanging out with him at his crib, it’s probably not going to get taped. Since Jim won’t be around to tell anyone what you said, if he succeeds you should be in good shape.
Also, “Well, I’d kill myself if I were you,” isn’t telling someone to do it, it’s just sharing an opinion. It’s not dishonest. You are never under any burden at law to lie to anyone… at most the law compels you not to answer, never to lie.