I used to work a shitty retail job, and there was the old guy who'd come in sometimes who we nicknamed "Magnum" (as in Magnum PI - dude had the moustache, and it seemed appropriate). I think he was part of some community watch organisation or something, and seemed to think that extended as far shoplifting prevention at our store (despite us having our own Paul Blart knock-off).
On the whole he was pretty harmless, but got warned by management a couple of times after he chased someone out of the store who he (incorrectly) thought was shoplifting. Guy seemed like he was maybe 80% there most of the time, so I guess wandering around the store cosplaying as a private detective a few hours a week kept him busy. He was a bit weird and a bit of a headache for the store manager, but I'd take him any day over the meth dealer who set up her office in the changing room or the 40 somethings who kept trying to score with the literal highschoolers working checkout