Grezzy is used when a person or a situation is greasy, shady or sketchy.
1) Person 1: Have you seen Charles' moustache?
Person 2: Yeah that's so grezzy, I can't even look at it.
2) Person 1: Dude, look at that creeper in the dark alley.
Person 2: Yeah I wouldn't walk there he looks so grezzy.
3) Person 1: Let's go to that cheap strip club downtown..
Person 2: Ew man, no way that place is too grezzy and the strippers are super grezz.