When I worked at a movie theater the time when the movies were showing was pretty much a gimmie because aside from wiping down the counter and maybe refilling the napkin dispenser, there were not a lot of job-related things we could be doing. Our theater only had two screens (two AMAZINGLY HUGE screens that were like the first two in the country to use THX), so even with slightly staggered start times, we still ended up with nice chunks of free time to spend reading or making hats out of the popcorn buckets. Of course, every now and then some peckish patron would wander out to the lobby in search of sustenace, so we had to be constantly ready to snap back to attention.

One sleepy summer day when we were showing some nonstarter like Guilty as Sin this old woman came out of the theater, digging in her pockets for change. She did seem a little fragile-looking, but she was capable of walking up to the counter, counting out her quarters, and asking for a box of Spree (all she could afford with her change), so we didn't think anything of that.

So she goes back in the theater with her candy, and ten minutes later she is dragged back out by a younger woman--her daughter--who proceeds to tear us a new one because her mother was diabetic and not supposed to have sugar and apparently it was our fault that we had not grilled her to discover this fact before selling her the candy. Seeing as how the mom was so out of it, we thought maybe the daughter might want to keep a closer eye on her, or even give her some sort of medic alert bracelet or sign to wear to warn people, because come on...we weren't exactly a bar checking IDs before serving alcohol or something. Luckily the mom was fine and didn't go into shock or anything.

It's difficult sometimes, obviously, to tell if a patron is all there. But sometimes it's pretty clear. Later in life I was working at a college book store, and just before I started there they had an incident with a patient from a nearby mental hospital who got out and went on his own little spree. The workers could tell something was a little off as soon as the guy shambled in, and their suspicions were confirmed when he sat down in a corner, pulled some dried leaves out of his pocket, spread them over his palms, and began to pore over them as if they were a map, saying, "I'm looking for precious rocks and gems."