Cack meaning shit, faeces or poo. Gash being a womans reproductive organ or vagina. Cack gash invariably means a vagina that has been covered in a man or womans shit. This usually happens when a man, after deciding against sex, opts to shit over the ladys vagina. The lady can become incensed and throw fits of rage as a result.
A plank doctor is a professional in the art of plank study. Plank doctors are recruited by organisations to seek out 'planks' in their workplaces. Planks being socially inept, smelly bastards. Plank doctors attempt to cleanse and heal these people, if a solution is not found the plank is usually fobbed off into a ditch.
Do you hear about Jimmy - a plank doctor came and took him away
Jim : Look at that ditch full of those dead planker bastards
Bob: Yeah those bloody plank doctors are mental