The acronym stands for Genuine Monkey Reaction. A physical reaction akin to the face of a suprised monkey, often in relevance to something that elicites an excited, bewildered, or humorous facial contortion.
GMRC: Acronym for "Good Manners and Right Conduct"
Good manners: saying PLEASE when asking for a favor; THANK YOU when you are pleased with a job well done! SORRY when you unintentionally hurt that someone doing the favor