pus gut

a fat bastard, someone who resembles a big pile of guts all swollen and vomit inspiring to view them

This one goes way back, probably to New England Yankees. It actually means someone with an inflated opinion of himself who lets the world know about it--a windbag. It also has an undertone of meaning someone who's basically an unworthy lazy slug. Not a pretty picture!

Someone who has suffered appendicitis, especially a ruptured appendix, thus filling their gut with pus.