Meaning quite the opposite of "nasty", which this word is commonly related to, it is an acronym for "nifty as fuck", it began as simply "naf", (i.e. "that burrito was pretty naf, man.") however upon making the word available with more ease, the suffix "-ty" was added on. Thus changing the acronym from "naf" to "nafty", giving it better use as it was intended, as an adjective. This is used to describe something seen as good, or as a more extreme form of "nifty".
If zombies were going to attack, I think we could set up a pretty nafty Zombie Smasher vehicle. It could run on zombies.
The act of giving someone a "Thug Nafty In Yo Mouf" is as follows:
The man is receiving oral sex, then proceeds to urinate AND ejaculate into the female's mouth. After he is done, he looks down at the dumb whore and says "I just 'Thug Naftied in yo mouf bitch! Now go make me a damn sandwich"
"HeyLisa, if you come over tonight, I'll give you a Thug Nafty In Yo Mouf."
A term used by ricers to define a car that is extremely low to the ground. Most of the time this will involve their car scraping on the ground whenever they drive it.