Cady Heron passes by the ROTC Guys lunch table.
ROTC Guys are a clique at North Shore High School. They are defined as such by Janis Ian in a map of the North Shore Cafeteria intended for Cady Heron's use.
When Janis gives a verbal description of the map, the film does not show this clique at that time.
ROTC stands for Reserve Officer Training Corps which is a program that helps students prepare for a career in the military, suggesting that the clique is full of strong, tough kids.