What is mean girls butter your muffin?

"Mean Girls" is a popular American teen comedy film released in 2004. It was directed by Mark Waters and written by Tina Fey. The movie revolves around the life of a high school girl named Cady Heron, who moves to the United States from Africa and finds herself caught in the world of "the Plastics," a clique of popular girls at her new school.

The phrase "butter your muffin" is a line spoken by Karen Smith, one of the members of the Plastics, in the movie. It is a slang term used to sexually arouse someone or to show attraction towards them. The line is often used as a famous quote from the movie and has become a part of popular culture.