Glen Coco is a fictional character in Mean Girls who is a student at North Shore High School. He has no dialogue and serves the plot in no way.
Although he's a small character that doesn't speak, one of the best quotes from the movie is about him. Most likely a junior along with the rest of the plastics being in Cady and Gretchen's class.
Damian: [delivering candy canes] Taylor Zimmermann, two for you. Glenn Coco? FOUR for you Glenn Coco! You go, Glenn Coco!"