To "nah dude" is to dismiss another quickly and efficiently. No further statement of clarification is necessary once one has been "nah duded." They should know why.
Example 1: My mom was all like "do the dishes" so I nah duded her:
Mom: Do the dishes
Me: Nah dude.
Example 2: My philosophy professor asked me if the ends justified the means so I had to nah dude him
Professor: BLAH BLAH BLAH
Me: Nah dude.
Example 3:
Friend 1: Hey, you want to go to Jimmy John's and get a lettuce wrap?
Friend 2: Nah dude.
A rare disorder related to Stockholm Syndrome where upon being mugged by a Hobo while taking a piss, the victim takes pity on the mugger and gives him a BJ. In an effort to comfort the Hobo and gain trust, the victim will swallow the Hobo's man custard. A bond develops between the mugger and victim, to such a level where, as a sign of gratitude, the Hobo returns the victims wallet (sans £60).
Mick: Dave, where you been?
Dave: Just been hangin' a piss in that seedy alley way, some cunt just stole my wallet
Mick: Right, so how do you explain the jizz running down the side of your mouth?
Dave: What? fuck that, someone get me a crowbar, I'm gonna go after the cunt who stole my wallet
Mick: Dave, face it, you're a Hobo Semen Eating Dude.
Dave: Dude...