Pertaining to the mindset many people have, the need to be near other people (even strangers), often at the disappointment of the strangers/foreign group.
How large numbers of people act in the same ways at the same times.
Parking your car in a space directly next to another, when the entire lot is empty. Also may be used effectively to describe a group's behavior when choosing a spot on an empty beach. If they lay their blanket within a few feet of you, they have demonstrated the herding mentality.
"Did you see where they just put their blanket?! It's practically on top of ours and the ENTIRE beach is empty."
"They totally have the herding mentality."