In mathematics, the Klein Bottle is a certain non-orientable surface, i.e. a surface (a two-dimensional topological space), for which there is no distinction between the "inside" and the "outside" of the surface. Its inside is its outside. It contains itself. A Klein bottle is a theoretical entity that exists only in 4 dimensions.
A Klein Asshole, aka Kleinhole, is someone who's assholishness has engulfed them to such a degree that it is no longer possible to tell where the Asshole begins or ends. As opposed to the Klein Bottle, Klein Assholes are very real and exist in 3 dimensions and are all around us.
Those guys from <rival town> aren't just assholes - they're fucking KLEIN ASSHOLES - EVERY ONE OF THEM.