A slob is somebody who doesn't have a clue about cleanliness, housekeeping, and/or hygiene. Typical of a slob, you will find molded dishes in the sink, food slopped all over the stove/counter. You will find rotten food in the refridgerator, mold in the bathroom, and dirty clothes scattered about on the floor. Typically, due to the living conditions, there will be insects/bugs/mites/bed-bugs, etc. A 'slob' goes beyond 'lazy' because the slob doesn't know HOW to clean properly, and is not just mearly lazy. A slob can work a full-time job, live on their own, etc. But their home/car/whatever is trashed.
He is such a slob, I just can't understand his lifestyle. It's so unhygienic that I can't go around his house, because I might catch the flu, bugs will nest under my skin, or something worse. The insects and mold are disgusting, and his clothes haven't been washed in 3 weeks.