For the love of the Emperor, how did we miss nasty, pus-filled, disease-carrying, bowel-voiding Nurgle?
Nurgle also makes an appearance in Warhammer. Also, Ogre and Beastman eating habits, and practically everything involving the Skaven, depending on your tolerance for rats; let's not get started on Clan Moulder's horrifying, painful and usually pointless "experiments" on living things.
Exalted: The Phylactery Womb. It's a little girl that stores Infernal exaltation spark inside her body... turning her into a bloated thing that oozes disgusting liquid from every orifice of her body. And this is one of the tamer description.
FATAL has a lot of game mechanics focusing on particular body parts. It can get rather disgusting and frightening rather quickly.