I believe someone IRL is subscribed to my profile here. I don't know this person's username but I suspect I will know it if I see it. Is there any way to see who has subscribed to you, and to control who is able to do so?
Try going to your profile by clicking on your name up on top where you sign in. Once there, in the left-hand column scroll down to Friends and Contacts and click on that. It should show you who is subscribed to you. Follow the directions to break the connection.