I've seen this phenomenon in places as diverse as a university physics department, several bars, a college radio station, a few schools, and a health food store. These volunteer/pest hybrids spend time in the place for their own odd reasons, end up taking on tasks for which they are not compensated, and eventually gain an inexplicable power.
In police and fire stations this is way too common, and probably just flat out bad for society, since wannabee cops and firefighters are actively dangerous people. Aside from those examples, mostly these characters are harmless and extremely annoying.
At the coffeehouse currently we have one. He's a pretty nice guy, on disability from a chronic illness, who has a lot of time to kill and appears to have some sort of OCD problem. He spends much of his day there and helps out. He constantly cleans up trash, arranges the tables in a tight grid with two chairs per table, and throws away all newspapers constantly. He runs off the teenaged kids who come there to eat their Wendys food and have french fry fights. He appears, in fact, to have declared himself Mayor of the Coffeehouse Patio.
It's hard to say what to think about this. The guy is harmless and pleasant, and means very well. He also, as he points out, needs something to do so he doesn't go nuts. Not being employable plus sitting around watching tv makes you something something. He rebuilds cars but doesn't do this constantly.
On the other hand, it's bizarre and unnerving to watch him go around lining up the tables again and emptying all the ashtrays and asking someone "Are you done with that?" more than once, and giving the employees and the manager advice, and telling some people to leave, and and and. It seems to be getting worse, too.
Any similar stories? I know gordonzola has bothersome cheese geeks at times, and most people who work in computer stores have a few of these at times. Tobacconists collect them, too..