A stubbornly dirty asshole.
When you've recently done a bowel movement, and you have to keep on wiping and wiping and wiping and wiping but it just won't get clean, always having poop on the toilet paper with each wipe.
Can be a very uncomfortable and annoying ailment. It is suggested that if you experience nang, you include more fibre in your diet.
"Oh man, I just missed my favourite show cause I was stuck on the toilet with a goddamn nang!"
"I need to buy extra toilet paper as I always seem to have a nang"