The maximum number of intersections of two polygons
  We investigate the maximum number of intersections between two polygons with p and q vertices, respectively, in the plane. The cases where p or q is even or the polygons do not have to be simple are quite easy and already known, but when p and q are both odd and both polygons are simple, the problem is more difficult. The conjectured maximum is (p-1)(q-1)+2 for all odd p and q. 
Felix G\"unther
math.CO cs.DM