One of the perils of the writing life, at least if you work in public, is that random people will talk to you. They will just sit down next to you and start talking, regardless of how busy you might happen to be. It might be a little old lady who wants to tell you all about her grandchildren, or someone who thinks you just need to know all of his political opinions in detail, or the fine points of some federal crime he's committed.
You might think that you could get around this sort of thing by just being really focused and making it obvious. I'm afraid you'd be wrong. Hunch over your laptop, furrow your brows, turn your eyes into fiery coals of rage- it still won't work. In fact, it will backfire. The more dementedly focused you look, the more psychotic the person who will feel compelled to sit next to you. Then, instead of hearing all about the best way to prune a geranium or some such thing, you can instead be treated to a hair-raising tale of hiding on a rooftop in some South American country for three days in order to prove that Johnny Cash was behind the Kennedy assassination.
There is, however, a silver lining, because many if not most of us freelance writers are also creative writers. They say that God never shuts a door without throwing you through a window (or something like that), and the window in this situation is that you no longer have to make up characters for your stories out of whole cloth. That man on the rooftop chasing Johnny Cash? You've got a short-story. The man with the eyes like Charlie Manson's, heading straight for you like he wants to talk? You could get a whole novel out of that guy.