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

When you eat dirt for the first time and leave your family to build a shack in the woods

The abdominal frontal protuberance characteristic of excessive drinkers of beer and food gorging.

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

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!