A lot of jobs involved dealing with regulars, or clients who are a bit on the weird or obsessed side. But for the most part, regulars are predictable enough that they don't ruffle feathers or get in the way.
The few outliers, however, can cross boundaries and get super weird, super fast. Some jobs, by merit of what they are, deal with more obsessive types than others. Train conductors and airplane pilots know this firsthand, as does anyone whose worked an event with historical re-enactors.
Folks jumped on a popular Reddit thread to share the most obsessive clients, regulars, or stalkers they've dealt with because of their job, and the stories range from hilarious to truly terrifying.
Train enthusiasts have been known to break into rail facilities and steal stuff off the more unique or rare equipment. It's a fairly regular occurrence... and often ruins it for the rest of us, as it'll put that piece of equipment out of circulation.