Arrange people in a circle (max 15-20 people per circle) and ask everyone to look down.
When the leader says "Look up" everyone must look up and immediately look at someone else in the circle. If two people are looking at each other, they must both scream and step out of the circle. Those that did not make eye contact with anyone continue to stare until the leader says "Look down". The game continues until there is only 2 or 3 people left in the circle.