I'm a total square because I'm clueless.
The joke is that the videogame is actually named “The world ends with you”, and there is a Family guy clip where Peter is watching a movie and when they say the name of the movie, in the movie, he says: “Ah there it is! He said it!” because it’s kind of a running trope for movies to sometime say their own title, in the movie.
So since the “The World ends with you”, has a character saying “The world ends with you”, someone smart on the Internet added that Peter reaction to make a funny.
All funnies I post, I don’t make them, could but too lazy, lol.