The opposite of the phrase "not too shabby." To perform certain tasks like a freaking idiot. When common sense is too overwhelming for you to bear that you mess up the easiest of tasks.
Max: did you see Carl try to paint today
Jason: yeah that was a total Shab Job
A crappy-a** wolf/retriever-type canine-breeding result in which said "half-and-half" mongrel pooch comes out wif weird-looking spots on its coat.
In "101 Dalmatians", Cruella is tricked into lettingthe stolen puppies pass by her unhindered due to their having rolled in ashes to crudely-but-effectively conceal their distinctive black-polka-dotted white coats; guess we could say that they had therefore turned themselves into Shab/Leopard-mix dogs.
Ava: Hello, Robert... Mmm, can you shab my nam?
Robert: What's. That.
Ava: When you put edible glitter on your PP and we have fast sex to sound of the wonderful Shabnam!
Robert: OK, that sounds so funnnnnnnnn! And soooooooooooooooo craaaaaaaazyyyy! I'm gonna put on Spotify on now and grab some glitter that you can eat!
Ava: YAYAYAYAYAYAAYYAAYAYYAYAYAAYYAYAYAYAYAAYAYAYAYAYA! I LOVE HER SO MUCH!!
Robert: Right, the first song is starting, LET'S DO IT!
*the two do it*