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.
Example:
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!!!"