Tales of the functionally insane?

You've heard functional illiterates and functional drug addicts, but what about those people who, while able to hold down a job, drive a car, and dress themselves, are clearly crazy? I worked in retail for a while so I certainly met a few, like the lady who insisted she was under constant surveillance and showed my as proof a text message on her phone consisting of *P *P *P. Proof, she claimed, that they were watching her use the bathroom. Or the guy that would bring items to the counter and ask for a discount (this was at Radio Shack). Not receiving one, would turn and walk out of the store without a word. Twice! Without interacting with them you might never realize they're nut. Please share your own stories of encounters with the Functionally Insane!!!!