1. Once you've crossed the line and realize the idiot in front of you is mentally ill.....briefly assess if you should stick around or claim you have an appointment for a haircut. This assessment should take into account: (a) if they are a relative....because you kinda have to stick by them, (b) if they are dangerous, (c) if this is bad-off mentally ill, and (d) how much time you really want to devote toward the situation.
2. Always try to suggest there's help somewhere for the guy/gal.
3. Let them talk about the issue as much as they want, but reassure them that you just aren't accepting of this condition being 'normal'.
4. Let them know in a nice way....you got time to hear them, but at the 20-minute point, they need to wrap up their confession, and get ready to hear your advice.
5. Sometimes, all the mentally ill person needs is a 20-minute session of listening, and probably a a cigarette or beer.
6. Always be polite, but try to avoid statements like 'you sound crazy'.
7. If they are already under treatment by some doctor.....don't go suggesting different treatment.