A person/group cannot stop mentioning/challenging/thinking about another person/group eventhough the other person/group doesn't even acknowledge their existence
Living in someone's head rent free. They are in your mindall 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
A phrase originally meaning whenever someone can't stop obsessively thinking about something or someone, particularly something unimportant, or someone who isn't even remotely thinking about them in return.
However, due to overuse by morons, has come to just be a regurgitated, automated response to criticism of something someone doesn't want criticized. Often used as a coping mechanism whenever an actual, intelligent rebuttal can't be made.
Person 1: "I don't like this restaurant. Every time I go there, the tables and chairs are sticky and the service gets my order wrong."
Person 2 (smugly believing they are somehow making a point): "Oh yeah? Well, that restaurant is living in your head RENT FREE!!!"