To live in the head of someone that can’t stop thinking about you or anything to do with you.

To live in the head of someone who can’t stop thinking about someone or what someone does, especially someone whom they say they hate.

The phenomenon of Woolwich arsenal fans being completely obsessed with Spurs, constantly talking about them and generally thinking about Tottenham Hotspur all the time. Whilst therest of the world barely knows who the Woolwich even are

An insult commonly used on various 4Chan boards.
It insinuates that the person being insulted lives "rent free" with his or her parents, and thus must be a NEET with no life.
Note that when used, insults like this will often either completely shut down an argument or turn it into a rapid back-and-forth flame war, derailing it.

Living in someone's head rent free. They are in your mind all the time and you are constantly thinking about them. All your thoughts are about them, and they have no idea. Usually happens when you have a big crush on someone

To live in someones head that can’t stop thinking about you.

Living in someone's head rent free. They are in your mind all the time and you are constantly thinking about them