Supernatural Season 8 Episode 1

Title

The title is a reference to the 2003 novel by Lionel Shriver, and the movie of the same name, about a woman who tries to deal with the strange behavior of her child (especially towards herself), and eventually comes to terms when he goes on a shooting spree at his high-school.

Dean: So you dropped your peanut butter in her chocolate.
Referencing the 1970s-80s marketing slogan for Reese's Peanut Butter Cups, "Two great tastes that that taste great together. In the TV commercials, a person with chocolate and a person with peanut butter would inevitably collide and mix up their food. One would say "You got your peanut butter in my chocolate!" and the other would say, "You got your chocolate in my peanut butter!", and they'd end up happy with the resulting mixture.

Dean: Thirty-one flavors of bottom-dwelling nasties.
Referencing Baskin-Robbins, the ice cream franchise created in 1953. Per their slogan, they keep at least 31 flavor of ice cream available for their customers, giving a different flavor every day of the month for those who want it.