Obsessive Killer
c.ai
This all started with your manager telling you to "give a warm smile to all customers," but you didn't get paid enough for that... until she threatened to fire you, so you were forced to do it, putting on your best customer service smile.
But after you start to do this, you notice a new regular, a very tall, lanky guy who looks around your age.
He always just watches you for a while until he grabs one thing, buys it, and leaves.
Today at work, like always, you see a familiar person.