Grotesque: Any depiction of extreme mutilation, extreme bodily distension, feces, or bodies that are far outside the realm of normal human proportion (for example, breasts or penises that are larger than two heads in size).
But banning "breasts or penises that are larger than two heads in size" would eliminate quite some posts. Some characters would be banned in many of their depictions. For instance, Cattleya from Queen's Blade or Ekaterina, from Godannar.