What do you say to someone that is suicidal?

First, acknowledge their feelings.  While they may be irrational, they are very real emotions. Tell them that you are worried about them and ask them to seek help. If they will not seek help, take steps to alert the appropriate people.  Do not ignore any verbal signs.  Do not keep it a secret.  Ask them to contact emergency services immediately.  The National Suicide Prevention Lifeline is 1-800-273-TALK