The Pac-Man Rule: When standing as a group of people, always leave room for 1 person to join your group.
Leaving room for new people when standing in a group is a physical way to show an inclusive and welcoming environment. It reduces the feeling of there being cliques, and allows people to integrate themselves into the community.
Your mission, if you choose to accept it, is to try and build the largest Pac-Man in the room. Invite new people into your groups, make new friends, and build a community full of people who feel included. We all benefit.
From: The Pac-Man Rule at Conferences