In episode 13 season 2 of Family Guy, titled "Road to Rhode Island", airing May 30th 2000, Chris delivered the iconic line, "Ahh! Get out of my head! Get out of my head!" After asking his sister Meg if she could guess the word he was thinking for the second time in presumably a 24hr period, the former occuring after 16:00 and the latter being the final scene at 21:40. Both times the word was "Kitty" despite his obviously facetious hints that it would not be Kitty. His lack of self awareness pairs with his low intelligence level to make it seem as if Meg's use of short term memory were absolute witchcraft. THIS HAS BECOME A WIDESPREAD JOKE AND GROWN TO BE A REFERENCE TO ANY TIME YOU MISUNDERSTAND A JOKE OR ARE THE LAST ONE TO REALIZE SOMETHING OBVIOUS. IT IS A SARCASTIC WAY OF ADMITTING A LACK OF PERCEPTION AS WELL AS IDENTIFYING ONE IN SOMEONE ELSE. The tone is important to signify the reference to the original, satirical caricature of low intelligence resulting from neglect that is Chris Griffin
A-"I'm thinking of a number between 1-10 but not 6, guess what it is"
B-"I really don't want to"
A-"You have to, you'll never get it"
B-"Fine, 6."
A-(In an absolutely terrified shriek) "Get out of my head!"