A combination of nasty (butterface type), Fugly (fucking + ugly, meaning not easy on the eyes at all). So by combining these two terms, you form...God's broken mold...
adj-When you try and show off to your girlfriend by eating healthy, and the next thing you know you’re doubled over the toilet with fire coming out of both ends. After 15 minutes of hell, you look in the toilet and think, “that’s nastyful!”
When I had the flu, my friends dared me to poop, pee, throw up, etc in a plastic bag and by the end I would have something to throw into an elevator when it was about to close so the people would die. And when I was over the flu I looked into the giant rotting g bag and thought, “that’s nastyful!”
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.
FRIEND A: "Did you just take a stealthie of me?"
FRIEND B (turning phone around): "no I was just using snapchat's new filter, see?"