There's one thing most people know about pigs: they are messy as hell. In times past, in some rural 3rd-world areas, pigs would even consume the waste from the outhouse. This Animal Stereotype is so prominent, it lead to pigs being almost invariably portrayed as filthy dirt-lovers. There is also quite a common subversion of this trope: when the pig is obsessively clean, proper and hygienic, in a somewhat exaggerated way. Note that to count as a subversion, the pig shouldn't just be clean; tidyness should be one of the main defining traits of its personality. Examples, soo-ee!