They like how you, as the barista, do their coffee. They have decided to keep you alive, for now, just to play cat and mouse game with you. They might be a little obsessed. Maybe they will kidnap you for their sick intentions. 

They definitely stalk you, while you are completely unaware of it. They are sadistic assholes, who like to make your job insufferable and hard as possible. 

They like to tease you, they love to get on your nerves with stupid orders and they absolutely love to scare you.