The condition in which a large number of people with no real direction or purpose suddenly find themselves in conflict with each other, and simultaneously decide - subconsciously - to meet in the middle, which somehow manages to only make things exponentially worse.

Easily prevented by situational awareness, which is generally checked at the door when entering consumer supercenters, convention halls, and other buildings/spaces which see generous amounts of human traffic.

The sort of thing that might happen at a 6-way intersection if the traffic light were broken.