A 'gus' can also be used to describe a person with insufficient wiping skills, resulting in him or her smelling strongly of feces - and with occasional smears of dung riding up the butt crack and lower back region.
That chick sitting ahead of me has insane swamp ass. There is a pool of booty juice left on the seat and she smells like fresh shit. What a gus! There is a trail of crap leading up her lower back.