A dense or oblivious person. Someone completely unaware of their surroundings, a clueless individual.
This is a term that originated in the Midwest. It refers to the hundreds of urbanites and suburbanites that can be seen walking out on melting ice cliffs that form into Lake Michigan beaches in the winter to take pictures or get a view. They ignore signs warning of the dangers of doing this and often bring their kids of dogs with them on the ice.